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/ko.json

@@ -975,7 +975,11 @@
     "exportPDF": "PDF 내보내기",
     "savedStatus": "저장됨",
     "dirtyStatus": "수정됨",
-    "completedLabel": "완료"
+    "completedLabel": "완료",
+    "notes.emptyNotebook": "빈 노트북",
+    "notes.emptyNotebookDesc": "이 노트북에 노트가 없습니다. +를 클릭하여 만드세요.",
+    "notes.noNoteSelected": "선택된 노트 없음",
+    "notes.selectOrCreateNote": "목록에서 노트를 선택하거나 새로 만드세요."
   },
   "pagination": {
     "next": "→",