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).

frontend/src/app/dashboard/DashboardSidebar.tsx

@@ -18,6 +18,7 @@ export function DashboardSidebar() {
   const { t } = useI18n();
 
   const isPro = ['pro', 'business', 'enterprise'].includes(user?.tier ?? '');
+  const isPaid = !!user?.tier && user.tier !== 'free';
   const navItems = isPro ? baseNavItems : baseNavItems.filter(item => !item.proOnly);
 
   return (
@@ -68,7 +69,8 @@ export function DashboardSidebar() {
         </div>
       )}
 
-      {/* Memento promo section */}
+      {/* Memento promo section — hidden for paying users */}
+      {!isPaid && (
       <a
         href={t('memento.url', { defaultValue: 'https://memento-note.com/' })}
         target="_blank"
@@ -88,6 +90,7 @@ export function DashboardSidebar() {
           </button>
         </div>
       </a>
+      )}
 
       {/* User section */}
       <div className="border-t border-black/5 dark:border-white/5">

frontend/src/app/dashboard/constants.ts

@@ -1,4 +1,4 @@
-import { FileText, Key, BookText, User, type LucideIcon } from 'lucide-react';
+import { FileText, BookText, User, type LucideIcon } from 'lucide-react';
 
 export interface NavItem {
   labelKey: string;
@@ -11,5 +11,6 @@ export const baseNavItems: NavItem[] = [
   { labelKey: 'dashboard.nav.translate', href: '/dashboard/translate', icon: FileText },
   { labelKey: 'dashboard.nav.profile', href: '/dashboard/profile', icon: User },
   { labelKey: 'dashboard.nav.glossaries', href: '/dashboard/glossaries', icon: BookText, proOnly: true },
-  { labelKey: 'dashboard.nav.apiKeys', href: '/dashboard/api-keys', icon: Key, proOnly: true },
+  // API Keys nav item temporarily removed per request — uncomment to restore.
+  // { labelKey: 'dashboard.nav.apiKeys', href: '/dashboard/api-keys', icon: Key, proOnly: true },
 ];

frontend/src/app/dashboard/translate/page.tsx

@@ -20,6 +20,7 @@ import { useNotification } from '@/components/ui/notification';
 import { useI18n } from '@/lib/i18n';
 import { API_BASE } from '@/lib/config';
 import { cn } from '@/lib/utils';
+import { useUser } from '../useUser';
 
 /* ── helpers ─────────────────────────────────────────────────────── */
 const FILE_ICONS: Record<string, React.ElementType> = {
@@ -74,6 +75,8 @@ export default function TranslatePage() {
   const submit = useTranslationSubmit();
   const { error: showError } = useNotification();
   const { t } = useI18n();
+  const { data: currentUser } = useUser();
+  const isPaid = !!currentUser?.tier && currentUser.tier !== 'free';
   const lastErrorRef = useRef<string | null>(null);
   const replaceInputRef = useRef<HTMLInputElement>(null);
   const dropzoneInputRef = useRef<HTMLInputElement>(null);
@@ -742,8 +745,8 @@ export default function TranslatePage() {
           </div>
         </div>
 
-        {/* ── MEMENTO PROMO BANNER ──────────────────────────────── */}
-        {(showUpload || showConfiguring || showFailed) && (
+        {/* ── MEMENTO PROMO BANNER — hidden for paying users ────── */}
+        {!isPaid && (showUpload || showConfiguring || showFailed) && (
           <a
             href={t('memento.url', { defaultValue: 'https://memento-note.com/' })}
             target="_blank"

frontend/src/test/constants.test.ts

@@ -10,10 +10,15 @@ describe('baseNavItems', () => {
     });
   });
 
-  it('should flag glossaries and apiKeys as proOnly', () => {
+  it('should flag glossaries as proOnly', () => {
     const glossaries = baseNavItems.find(item => item.href === '/dashboard/glossaries');
-    const apiKeys = baseNavItems.find(item => item.href === '/dashboard/api-keys');
     expect(glossaries?.proOnly).toBe(true);
-    expect(apiKeys?.proOnly).toBe(true);
+  });
+
+  it('should currently omit apiKeys nav item (temporarily removed)', () => {
+    // The apiKeys nav item is temporarily commented out in constants.ts.
+    // If you re-enable it, update this test to assert its presence.
+    const apiKeys = baseNavItems.find(item => item.href === '/dashboard/api-keys');
+    expect(apiKeys).toBeUndefined();
   });
 });