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/zh.json

@@ -998,7 +998,11 @@
     "exportPDF": "导出PDF",
     "savedStatus": "已保存",
     "dirtyStatus": "已修改",
-    "completedLabel": "已完成"
+    "completedLabel": "已完成",
+    "notes.emptyNotebook": "空笔记本",
+    "notes.emptyNotebookDesc": "此笔记本没有笔记。点击 + 创建一个。",
+    "notes.noNoteSelected": "未选择笔记",
+    "notes.selectOrCreateNote": "从列表中选择笔记或创建新笔记。"
   },
   "pagination": {
     "next": "→",