fix: i18n complet — mobile, backlinks, undo/redo, content-area

- mobile-action-sheet.tsx: 15 chaînes → t()
- wikilinks-backlinks-panel.tsx: 3 chaînes → t() + import useLanguage
- note-content-area.tsx: 'Cliquez pour éditer' → t()
- undo-redo-feedback-extension.ts: strings → options configurables
- i18n FR/EN: 11 nouvelles clés (mobile.*, editor.*)
- SlashPreview et SlashCommand: déjà OK (i18n via localCommands)

memento-note/locales/en.json

@@ -2617,6 +2617,16 @@
     "slashLivingBlock": "Living Block",
     "slashLivingBlockDesc": "Insert from another note",
     "frequentCommands": "★ Frequent",
+    "mobileBlockActions": "Block Actions",
+    "mobileSelectAll": "Select All",
+    "mobileDuplicate": "Duplicate",
+    "mobileDelete": "Delete",
+    "mobileAiNote": "AI Note",
+    "mobileConvertFormat": "Convert Format",
+    "mobileParagraph": "Paragraph",
+    "mobileQuote": "Quote",
+    "editorBacklinks": "Incoming Links",
+    "editorClickToEdit": "Click to edit",
     "exercisesLoading": "Generating exercises...",
     "exercisesGenerated": "exercises created!",
     "aiGenerateExercises": "Generate exercises",