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/src/stores/push.ts

@@ -1,11 +1,12 @@
 import { defineStore } from 'pinia'
 import { ref } from 'vue'
 
-function urlBase64ToUint8Array(base64String: string): Uint8Array {
+function urlBase64ToUint8Array(base64String: string): Uint8Array<ArrayBuffer> {
   const padding = '='.repeat((4 - (base64String.length % 4)) % 4)
   const base64 = (base64String + padding).replace(/-/g, '+').replace(/_/g, '/')
   const rawData = window.atob(base64)
-  const outputArray = new Uint8Array(rawData.length)
+  const buf = new ArrayBuffer(rawData.length)
+  const outputArray = new Uint8Array<ArrayBuffer>(buf)
   for (let i = 0; i < rawData.length; ++i) {
     outputArray[i] = rawData.charCodeAt(i)
   }