TipTap editor, version history, search, attachments — and a cleanup

The app is meant to run in daily private use now, so this pass was mostly
about the ways it could quietly lose data.

Reliability and security:
- the server no longer invents a JWT_SECRET or ENCRYPTION_KEY when one is
  missing; it refuses to start. The old fallback silently made every stored
  note unreadable after a restart.
- notes are encrypted with AES-256-GCM (v2:); existing CBC bodies still read.
- login is rate limited and compares against a dummy hash when the user does
  not exist, so timing does not reveal who is registered.
- a server response issued before a local save is never adopted. This had
  already eaten drawing strokes and note links; sync.hasPendingWrites() now
  guards every path that takes a body from the server.

Editor and features:
- TipTap replaces the contenteditable editor: tables, task lists, and links
  to other notes and notebooks, with a backlinks bar on the target.
- content format v2 ({v:2,doc}); v1 {html,tasks} bodies migrate on open.
- version history: the state before each write is snapshotted, coalesced
  into 5-minute windows, 50 versions or 90 days per note.
- full-text search runs in the client, because the server cannot read
  encrypted bodies and a server index would defeat the encryption.
- image attachments are stored by SHA-256 and deduplicated; the client
  fetches them authenticated and caches the blob, so they work offline.
- drawings are vector strokes in a fixed 1200x1600 page space and now look
  the same on every screen (0.0-0.2% deviation across four widths).
- login is by username; existing email accounts migrate automatically.

Operations:
- data lives on host bind mounts, not Docker volumes, so Proxmox Backup
  covers it. Back up .env with it — without ENCRYPTION_KEY the dump is
  unreadable.

Structure:
- NoteApp.jsx is gone. App.jsx now holds only where the user is; note data,
  search, layout, history and drag each live behind a hook, and the four
  panes are stateless.
- the whole data layer is TypeScript, with 81 unit tests concentrated on
  the places that have actually broken.
- fixed along the way: the browser back button had a dead press, because
  restoring a history entry pushed a duplicate one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/package.json

@@ -6,14 +6,40 @@
   "scripts": {
     "dev": "vite",
     "build": "vite build",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "typecheck": "tsc --noEmit",
+    "format": "prettier --write 'src/**/*.{js,jsx,ts,tsx,css}'"
   },
   "dependencies": {
+    "@tiptap/extension-image": "^2.27.2",
+    "@tiptap/extension-link": "^2.27.2",
+    "@tiptap/extension-placeholder": "^2.27.2",
+    "@tiptap/extension-table": "^2.27.2",
+    "@tiptap/extension-table-cell": "^2.27.2",
+    "@tiptap/extension-table-header": "^2.27.2",
+    "@tiptap/extension-table-row": "^2.27.2",
+    "@tiptap/extension-task-item": "^2.27.2",
+    "@tiptap/extension-task-list": "^2.27.2",
+    "@tiptap/extension-underline": "^2.27.2",
+    "@tiptap/html": "^2.27.2",
+    "@tiptap/pm": "^2.27.2",
+    "@tiptap/react": "^2.27.2",
+    "@tiptap/starter-kit": "^2.27.2",
+    "@tiptap/suggestion": "^2.27.2",
     "react": "^18.3.1",
     "react-dom": "^18.3.1"
   },
   "devDependencies": {
+    "@types/react": "^18.3.31",
+    "@types/react-dom": "^18.3.7",
     "@vitejs/plugin-react": "^4.3.1",
-    "vite": "^5.4.0"
+    "fake-indexeddb": "^6.2.5",
+    "jsdom": "^25.0.1",
+    "prettier": "^3.9.6",
+    "typescript": "^5.9.3",
+    "vite": "^5.4.0",
+    "vitest": "^2.1.9"
   }
-}
+}