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).

tests/test_chart_translation_prompt.py

@@ -0,0 +1,50 @@
+"""Verify all 3 provider prompts are identical and contain chart-translation rules.
+
+This is a regression test for the bug where chart titles/legends/category labels
+were left untranslated because the system prompt was too ambiguous about
+"proper nouns or brand names".
+"""
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from services.providers.deepseek_provider import DEFAULT_TRANSLATION_PROMPT as P1
+from services.providers.minimax_provider import DEFAULT_TRANSLATION_PROMPT as P3
+from services.providers.openai_provider import DEFAULT_TRANSLATION_PROMPT as P2
+
+REQUIRED_PHRASES = [
+    "Chart elements",
+    "MUST always be translated",
+    "Translate month and weekday abbreviations",
+    "Jan",
+    "janvier",
+    "Keep ONLY real proper nouns",
+    "Google, Microsoft",
+    "API, URL, HTTP, JSON",
+]
+
+
+def test_all_prompts_identical():
+    assert P1 == P2 == P3, "All 3 provider prompts must be identical"
+
+
+def test_prompt_contains_required_rules():
+    for phrase in REQUIRED_PHRASES:
+        assert phrase in P1, f"Missing rule: {phrase!r}"
+
+
+def test_prompt_drops_old_ambiguous_rule():
+    # The old "If the text contains proper nouns or brand names" rule was
+    # the root cause of chart labels not being translated. The new prompt
+    # uses a more specific rule that lists what counts as a proper noun.
+    assert "If the text contains proper nouns or brand names" not in P1, (
+        "Old ambiguous rule still present — chart labels will be skipped again"
+    )
+
+
+if __name__ == "__main__":
+    test_all_prompts_identical()
+    test_prompt_contains_required_rules()
+    test_prompt_drops_old_ambiguous_rule()
+    print("All prompt regression tests passed.")

tests/test_excel_chart_sheet_refs.py

@@ -0,0 +1,138 @@
+"""Regression tests for the bug where translated Excel chart <c:f> references
+kept pointing at the original (now-renamed) sheet name, causing the chart
+to render as zero/empty series after translation.
+
+This is a real bug: see e.g. test_excel.xlsx where the chart references
+'Sales 2024'!$D$2:$D$61 but the sheet is renamed to "Chiffre d'affaires
+par produit" — the chart then shows 0 for every data point.
+"""
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from lxml import etree
+
+from translators.excel_translator import ExcelTranslator
+
+NS_C = "http://schemas.openxmlformats.org/drawingml/2006/chart"
+
+
+def _build_chart_xml(series_refs):
+    """Helper: build a chart XML with the given <c:f> strings."""
+    sers = "\n".join(
+        f"<c:ser><c:tx><c:strRef><c:f>{ref}</c:f></c:strRef></c:tx>"
+        f"<c:cat><c:strRef><c:f>{ref}</c:f></c:strRef></c:cat>"
+        f"<c:val><c:numRef><c:f>{ref}</c:f></c:numRef></c:val></c:ser>"
+        for ref in series_refs
+    )
+    return f"""<c:chartSpace xmlns:c="{NS_C}" xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
+    <c:chart>
+        <c:plotArea><c:lineChart>{sers}</c:lineChart></c:plotArea>
+    </c:chart>
+</c:chartSpace>"""
+
+
+def test_quoted_sheet_name_with_apostrophe_in_new_name():
+    r = ExcelTranslator._rewrite_sheet_ref(
+        "'Sales 2024'!$D$2:$D$61",
+        {"Sales 2024": "Chiffre d'affaires par produit"},
+    )
+    assert r == "'Chiffre d''affaires par produit'!$D$2:$D$61", f"got: {r!r}"
+
+
+def test_unquoted_sheet_name_simple():
+    r = ExcelTranslator._rewrite_sheet_ref(
+        "Sheet1!$A$1",
+        {"Sheet1": "Feuille1"},
+    )
+    assert r == "Feuille1!$A$1", f"got: {r!r}"
+
+
+def test_new_name_with_space_gets_quoted():
+    r = ExcelTranslator._rewrite_sheet_ref(
+        "Sheet1!$A$1",
+        {"Sheet1": "Ma Feuille"},
+    )
+    assert r == "'Ma Feuille'!$A$1", f"got: {r!r}"
+
+
+def test_name_not_in_mapping_unchanged():
+    r = ExcelTranslator._rewrite_sheet_ref(
+        "Other!$A$1",
+        {"Sheet1": "Feuille1"},
+    )
+    assert r == "Other!$A$1", f"got: {r!r}"
+
+
+def test_empty_mapping_is_noop():
+    r = ExcelTranslator._rewrite_sheet_ref("Sheet1!$A$1", {})
+    assert r == "Sheet1!$A$1", f"got: {r!r}"
+
+
+def test_no_bang_is_noop():
+    r = ExcelTranslator._rewrite_sheet_ref("just_a_label", {"x": "y"})
+    assert r == "just_a_label", f"got: {r!r}"
+
+
+def test_real_chart_xml_all_refs_rewritten():
+    chart_xml = etree.fromstring(_build_chart_xml(["Sheet1!$B$1"]))
+    n = ExcelTranslator._rewrite_sheet_refs_in_chart(chart_xml, {"Sheet1": "Ma Feuille"})
+    assert n == 3, f"expected 3 rewrites, got {n}"
+    refs = [f.text for f in chart_xml.iter(f"{{{NS_C}}}f")]
+    assert refs == [
+        "'Ma Feuille'!$B$1",
+        "'Ma Feuille'!$B$1",
+        "'Ma Feuille'!$B$1",
+    ], f"got: {refs}"
+
+
+def test_real_chart_xml_apostrophe_escaped_in_new_name():
+    chart_xml = etree.fromstring(_build_chart_xml(["Sheet1!$B$1"]))
+    n = ExcelTranslator._rewrite_sheet_refs_in_chart(
+        chart_xml, {"Sheet1": "Chiffre d'affaires"}
+    )
+    assert n == 3
+    refs = [f.text for f in chart_xml.iter(f"{{{NS_C}}}f")]
+    assert all(r == "'Chiffre d''affaires'!$B$1" for r in refs), f"got: {refs}"
+
+
+def test_partial_mapping_leaves_other_refs_intact():
+    """When only one sheet is renamed, refs to other sheets must stay."""
+    chart_xml = etree.fromstring(
+        _build_chart_xml(["Sheet1!$A$1", "Sheet2!$B$1"])
+    )
+    n = ExcelTranslator._rewrite_sheet_refs_in_chart(
+        chart_xml, {"Sheet1": "Feuille1"}
+    )
+    # 3 refs to Sheet1 (one series) are rewritten; 3 refs to Sheet2 stay.
+    assert n == 3, f"expected 3 rewrites, got {n}"
+    refs = [f.text for f in chart_xml.iter(f"{{{NS_C}}}f")]
+    assert "Feuille1!$A$1" in refs
+    assert "Sheet2!$B$1" in refs
+
+
+def test_multiple_series_renamed():
+    """When several sheets are renamed, refs to any of them get updated."""
+    chart_xml = etree.fromstring(
+        _build_chart_xml(["Sheet1!$A$1", "Sheet2!$B$1", "Sheet3!$C$1"])
+    )
+    n = ExcelTranslator._rewrite_sheet_refs_in_chart(
+        chart_xml,
+        {"Sheet1": "F1", "Sheet2": "F2", "Sheet3": "F3"},
+    )
+    assert n == 9, f"expected 9 rewrites (3 series x 3 refs each), got {n}"
+
+
+if __name__ == "__main__":
+    test_quoted_sheet_name_with_apostrophe_in_new_name()
+    test_unquoted_sheet_name_simple()
+    test_new_name_with_space_gets_quoted()
+    test_name_not_in_mapping_unchanged()
+    test_empty_mapping_is_noop()
+    test_no_bang_is_noop()
+    test_real_chart_xml_all_refs_rewritten()
+    test_real_chart_xml_apostrophe_escaped_in_new_name()
+    test_partial_mapping_leaves_other_refs_intact()
+    test_multiple_series_renamed()
+    print("All chart sheet-ref rewrite tests passed.")