Upgrade all major frontend dependencies

- TipTap 2 → 3: Extension from @tiptap/core, Placeholder from
  @tiptap/extensions, TaskList/TaskItem from @tiptap/extension-list,
  link: false in StarterKit (now bundles Link), @tiptap/core added
- marked 15 → 17: heading renderer updated to tokens/parseInline API
- Pinia 2 → 3, Vue Router 4 → 5 (no code changes required)
- Vite 6 → 7, @vitejs/plugin-vue 5 → 6, vue-tsc 2 → 3
- TypeScript 5.6 → 5.9: fixed Uint8Array<ArrayBuffer> strictness in
  push.ts, removed unused bodyEl ref in NoteViewerView.vue
- .npmrc: legacy-peer-deps=true for TipTap v3 peer dep resolution

TipTap 3 new capabilities now available: static renderer
(createStaticRenderer), MarkViews, @tiptap/extensions package.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/package.json

@@ -9,27 +9,27 @@
     "preview": "vite preview"
   },
   "dependencies": {
-    "@tiptap/extension-link": "^2.11.0",
-    "@tiptap/extension-placeholder": "^2.11.0",
-    "@tiptap/extension-task-item": "^2.27.2",
-    "@tiptap/extension-task-list": "^2.27.2",
-    "@tiptap/pm": "^2.11.0",
-    "@tiptap/starter-kit": "^2.11.0",
-    "@tiptap/suggestion": "^2.11.0",
-    "@tiptap/vue-3": "^2.11.0",
+    "@tiptap/core": "^3.0.0",
+    "@tiptap/extension-link": "^3.0.0",
+    "@tiptap/extension-list": "^3.0.0",
+    "@tiptap/extensions": "^3.0.0",
+    "@tiptap/pm": "^3.0.0",
+    "@tiptap/starter-kit": "^3.0.0",
+    "@tiptap/suggestion": "^3.0.0",
+    "@tiptap/vue-3": "^3.0.0",
     "d3": "^7",
     "dompurify": "^3.1.0",
-    "marked": "^15.0.0",
-    "pinia": "^2.2.0",
+    "marked": "^17.0.0",
+    "pinia": "^3.0.0",
     "vue": "3.5.30",
-    "vue-router": "^4.4.0"
+    "vue-router": "^5.0.0"
   },
   "devDependencies": {
     "@types/d3": "^7",
     "@types/dompurify": "^3.0.0",
-    "@vitejs/plugin-vue": "^5.1.0",
-    "typescript": "~5.6.0",
-    "vite": "^6.0.0",
-    "vue-tsc": "^2.1.0"
+    "@vitejs/plugin-vue": "^6.0.0",
+    "typescript": "~5.9.0",
+    "vite": "^7.0.0",
+    "vue-tsc": "^3.0.0"
   }
 }