fix(translate): chart labels, sheet-refs, sheet-name offset, paid-user Memento

Multiple translation bugs in Word/Excel/PPTX that caused chart elements
to be left untranslated or charts to render as empty series.

Backend
-------
* providers (deepseek/openai/minimax): tighten system prompt so the LLM
  actually translates chart titles/axis labels/legend/category labels,
  month abbreviations, and clarifies what counts as a 'real' proper noun
  (people/place/company/product names) vs. technical labels. Old rule
  'keep proper nouns unchanged' was being read too broadly by the model
  and caused chart text to be skipped.
* excel_translator.py:
  - Sheet reference rewrite: when a sheet is renamed, the chart XML's
    c:f refs (e.g. 'Sales 2024'!$D$2:$D$61) are now rewritten to the
    new name with proper apostrophe escaping (Chiffre d'affaires ->
    'Chiffre d''affaires') and auto-quoting when the new name contains
    spaces or special chars. Without this, the chart points at a sheet
    that no longer exists and renders 0/empty series.
  - Sheet name offset bug: sheet_name_offset was computed after chart
    text was appended to text_elements, causing sheet names to receive
    chart text translations. Now captured BEFORE sheet names are added.
* New tests:
  - test_excel_chart_sheet_refs.py (10 unit tests, synthetic inputs)
  - test_chart_translation_prompt.py (3 contract tests on the prompt)

Frontend
--------
* DashboardSidebar / translate/page: hide the Memento promo section
  for paying users (tier != 'free').
* constants.ts: temporarily comment out the 'CLES API' nav item.
  Update constants.test.ts to match the new state.

All fixes are generic - no file-specific hardcoding, edge cases covered
(empty mapping, missing bang, apostrophe escaping, partial renames,
multi-series).

translators/excel_translator.py

@@ -198,16 +198,24 @@ class ExcelTranslator:
                         }
                     )
 
+            # Record the position where sheet names start in text_elements.
+            # We need this to extract the right slice of translated_texts
+            # AFTER chart text has been appended. Otherwise the offset
+            # calculation drifts and sheet names get chart translations.
+            sheet_name_offset = len(text_elements)
+
             for sheet_name in sheet_names_to_translate:
                 text_elements.append((sheet_name, None))
 
-            # Collect chart text from ZIP
+            # Collect chart text from ZIP (appended AFTER sheet names)
             self._collect_charts_from_zip(input_path, text_elements, chart_translations)
 
             if text_elements:
                 texts = [elem[0] for elem in text_elements]
                 total_texts = len(texts)
-                sheet_name_offset = total_texts - len(sheet_names_to_translate)
+                # sheet_name_offset was captured before sheet names + chart text
+                # were appended, so it already points at the start of the sheet
+                # name block. No re-derivation needed.
 
                 _log_info(
                     "excel_batch_translation_start",
@@ -317,9 +325,16 @@ class ExcelTranslator:
                     details={"file_name": output_path.name, "error": str(e)},
                 )
 
-            # Re-inject chart translations into the .xlsx ZIP
-            if chart_translations:
-                self._apply_chart_translations(output_path, chart_translations)
+            # Re-inject chart translations into the .xlsx ZIP.
+            # We always pass the sheet_name_mapping so chart <c:f> references
+            # are updated when sheet names were translated — otherwise the
+            # chart would keep pointing at the old (now-missing) sheet and
+            # render as empty/zero series.
+            self._apply_chart_translations(
+                output_path,
+                chart_translations,
+                sheet_name_mapping=sheet_name_mapping or None,
+            )
 
             workbook.close()
 
@@ -739,18 +754,27 @@ class ExcelTranslator:
         except Exception:
             return None
 
-    def _apply_chart_translations(self, output_path: Path, chart_translations: List[Dict[str, Any]]) -> None:
+    def _apply_chart_translations(
+        self,
+        output_path: Path,
+        chart_translations: List[Dict[str, Any]],
+        sheet_name_mapping: Optional[Dict[str, str]] = None,
+    ) -> None:
         """Re-inject chart translations into the .xlsx ZIP.
 
         Uses the `element_path` collected during `_collect_charts_from_zip`
         to target each element precisely. Falls back to string matching
         for entries that predate the path-based collection.
+
+        Also rewrites `<c:f>` references inside chart XML when sheet names
+        were translated — otherwise the chart keeps pointing at the old
+        sheet name and renders empty (zero) data.
         """
-        if not chart_translations:
+        if not chart_translations and not sheet_name_mapping:
             return
 
         translated_entries = [e for e in chart_translations if 'translated' in e and e['translated']]
-        if not translated_entries:
+        if not translated_entries and not sheet_name_mapping:
             return
 
         _NS_A = "http://schemas.openxmlformats.org/drawingml/2006/main"
@@ -763,6 +787,18 @@ class ExcelTranslator:
                 chart_files_to_update[cf] = []
             chart_files_to_update[cf].append(entry)
 
+        # If we have sheet renames, we must walk every chart file (even ones
+        # with no text translations) so the <c:f> references are updated.
+        if sheet_name_mapping:
+            # We need the list of chart files; peek into the zip to find them.
+            try:
+                with zipfile.ZipFile(output_path, 'r') as zf_peek:
+                    for name in zf_peek.namelist():
+                        if name.startswith('xl/charts/') and name.endswith('.xml'):
+                            chart_files_to_update.setdefault(name, [])
+            except Exception:
+                pass
+
         try:
             with zipfile.ZipFile(output_path, 'r') as zf_in:
                 existing_entries = zf_in.namelist()
@@ -789,6 +825,14 @@ class ExcelTranslator:
                                                 if v_elem.text and v_elem.text.strip() == entry['original']:
                                                     v_elem.text = entry['translated']
                                                     break
+
+                                # Rewrite sheet references in <c:f> when sheet
+                                # names were translated. Without this, charts
+                                # point at sheets that no longer exist and
+                                # render as zero/empty series.
+                                if sheet_name_mapping:
+                                    self._rewrite_sheet_refs_in_chart(chart_xml, sheet_name_mapping)
+
                                 data = etree.tostring(chart_xml, xml_declaration=True, encoding='UTF-8', standalone=True)
                             except Exception as e:
                                 _log_error("excel_chart_update_error", chart_file=item, error=str(e))
@@ -798,11 +842,86 @@ class ExcelTranslator:
             with open(output_path, 'wb') as f:
                 f.write(buf.getvalue())
 
-            _log_info("excel_charts_translated", chart_files=len(chart_files_to_update), translations=len(translated_entries))
+            _log_info(
+                "excel_charts_translated",
+                chart_files=len(chart_files_to_update),
+                translations=len(translated_entries),
+                sheet_refs_rewritten=len(sheet_name_mapping or {}),
+            )
 
         except Exception as e:
             _log_error("excel_chart_zip_rewrite_error", error=str(e))
 
+    @staticmethod
+    def _quote_sheet_name_for_ref(name: str) -> str:
+        """Return the sheet name as it must appear inside a chart <c:f> reference.
+
+        Excel requires single-quoting when the name contains spaces or any of
+        `:\\/?*[]`, and any single quote inside the name must be doubled.
+        """
+        if not name:
+            return name
+        needs_quote = any(c in name for c in " :\\/?*[]") or " " in name
+        escaped = name.replace("'", "''")
+        return f"'{escaped}'" if needs_quote else escaped
+
+    @classmethod
+    def _rewrite_sheet_ref(cls, ref: str, sheet_name_mapping: Dict[str, str]) -> str:
+        """Rewrite a single chart <c:f> reference to use translated sheet names.
+
+        Handles both quoted (`'Sheet 1'!A1`) and unquoted (`Sheet1!A1`) forms.
+        If the sheet name is not in the mapping, returns ref unchanged.
+        """
+        if not sheet_name_mapping or not ref or '!' not in ref:
+            return ref
+
+        if ref.startswith("'"):
+            # Find the closing single quote that ends the sheet name.
+            # Per the ECMA-376 grammar, the inner `'` is escaped as `''`,
+            # so we can safely scan for the next unescaped `'`.
+            i = 1
+            while i < len(ref):
+                if ref[i] == "'" and i + 1 < len(ref) and ref[i + 1] == "'":
+                    i += 2  # skip escaped apostrophe
+                    continue
+                if ref[i] == "'":
+                    break
+                i += 1
+            if i >= len(ref) or ref[i] != "'":
+                return ref
+            sheet_name = ref[1:i]
+            rest = ref[i + 1:]  # starts with "!<cellref>"
+        else:
+            bang = ref.index('!')
+            sheet_name = ref[:bang]
+            rest = ref[bang:]
+
+        new_name = sheet_name_mapping.get(sheet_name)
+        if not new_name or new_name == sheet_name:
+            return ref
+
+        return cls._quote_sheet_name_for_ref(new_name) + rest
+
+    @classmethod
+    def _rewrite_sheet_refs_in_chart(
+        cls, chart_xml, sheet_name_mapping: Dict[str, str]
+    ) -> int:
+        """Walk all <c:f> in the chart and rewrite those pointing at renamed sheets.
+
+        Returns the number of references rewritten (for logging/tests).
+        """
+        _NS_C = "http://schemas.openxmlformats.org/drawingml/2006/chart"
+        rewritten = 0
+        for f_elem in chart_xml.iter(f'{{{_NS_C}}}f'):
+            original = f_elem.text
+            if not original or '!' not in original:
+                continue
+            updated = cls._rewrite_sheet_ref(original, sheet_name_mapping)
+            if updated != original:
+                f_elem.text = updated
+                rewritten += 1
+        return rewritten
+
     def _translate_images(self, worksheet: Worksheet, target_language: str) -> None:
         """
         Translate text in images using vision model.