fix: replace hardcoded French strings in notes-tabs-view with i18n

- Empty notebook placeholder: "Carnet vide" → t('notes.emptyNotebook')
- No note selected: "Aucune note sélectionnée" → t('notes.noNoteSelected')
- Descriptions replaced with t('notes.emptyNotebookDesc'), t('notes.selectOrCreateNote')
- Removed French fallback on newNote button title
- Added 4 new i18n keys to all 15 locales

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/locales/en.json

@@ -157,7 +157,11 @@
     "exportPDF": "Export PDF",
     "savedStatus": "Saved",
     "dirtyStatus": "Modified",
-    "completedLabel": "Completed"
+    "completedLabel": "Completed",
+    "notes.emptyNotebook": "Empty notebook",
+    "notes.emptyNotebookDesc": "This notebook has no notes. Click + to create one.",
+    "notes.noNoteSelected": "No note selected",
+    "notes.selectOrCreateNote": "Select a note from the list or create a new one."
   },
   "pagination": {
     "previous": "←",