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/pl.json

@@ -1042,7 +1042,11 @@
     "exportPDF": "Eksportuj PDF",
     "savedStatus": "Zapisano",
     "dirtyStatus": "Zmodyfikowano",
-    "completedLabel": "Ukończone"
+    "completedLabel": "Ukończone",
+    "notes.emptyNotebook": "Pusty notatnik",
+    "notes.emptyNotebookDesc": "Ten notatnik nie ma notatek. Kliknij + aby utworzyć.",
+    "notes.noNoteSelected": "Nie wybrano notatki",
+    "notes.selectOrCreateNote": "Wybierz notatkę z listy lub utwórz nową."
   },
   "pagination": {
     "next": "→",