Add companion kitten — reactive corner mascot

A cozy bottom-right mascot that reacts to the writing session: cheers on
accepted suggestions and word-count milestones, drops Mandarin-first writing
tips, suggests screen breaks after long stretches, and naps when idle.

- useCompanion: library-agnostic behavior engine (priority + cooldown paced
  so it never nags); tips.ts holds all copy, bilingual zh-first.
- LottiePlayer wraps lottie-web's light build (offline, no eval/CDN) so it
  bundles into the Go binary. Ships with an emoji-kitten placeholder per mood;
  dropping a Lottie cat JSON into animations/index.ts is the only swap needed.
- Speech bubble uses the CJK-first font stack (spec Note #17).

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/package.json

@@ -9,15 +9,16 @@
     "preview": "vite preview"
   },
   "dependencies": {
-    "react": "^19.1.0",
-    "react-dom": "^19.1.0",
-    "@tiptap/react": "^2.11.5",
-    "@tiptap/pm": "^2.11.5",
-    "@tiptap/starter-kit": "^2.11.5",
-    "@tiptap/extension-underline": "^2.11.5",
-    "@tiptap/extension-text-align": "^2.11.5",
+    "@tiptap/extension-character-count": "^2.11.5",
     "@tiptap/extension-placeholder": "^2.11.5",
-    "@tiptap/extension-character-count": "^2.11.5"
+    "@tiptap/extension-text-align": "^2.11.5",
+    "@tiptap/extension-underline": "^2.11.5",
+    "@tiptap/pm": "^2.11.5",
+    "@tiptap/react": "^2.11.5",
+    "@tiptap/starter-kit": "^2.11.5",
+    "lottie-web": "^5.13.0",
+    "react": "^19.1.0",
+    "react-dom": "^19.1.0"
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.0.0",