feat(sidebar): add per-page hide toggle with more options dropdown

- Add ``` button in sidebar header with dropdown menu
- Add "Hide sidebar on this page" option with per-page localStorage state
- Show edge indicator (14px chevron) on left when hidden per-page
- Show brief toast notification when hiding
- Fix container margin not resetting when sidebar is per-page hidden
- Add i18n translations for all 10 locales

locales/zh-TW.json

@@ -953,9 +953,13 @@
     },
     "sidebar": {
         "modelRoot": "根目錄",
+        "moreOptions": "更多選項",
         "collapseAll": "全部摺疊資料夾",
         "pinSidebar": "固定側邊欄",
         "unpinSidebar": "取消固定側邊欄",
+        "hideOnThisPage": "隱藏此頁面側邊欄",
+        "showSidebar": "顯示側邊欄",
+        "sidebarHiddenNotification": "{page}頁面的資料夾側邊欄已隱藏",
         "switchToListView": "切換至列表檢視",
         "switchToTreeView": "切換到樹狀檢視",
         "recursiveOn": "包含子資料夾",