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/src/App.tsx

@@ -5,6 +5,7 @@ import { useCheckpoint } from './hooks/useCheckpoint'
 import { DocList } from './components/DocList/DocList'
 import { EditorCore, type EditorChange } from './components/Editor/EditorCore'
 import { StatusBar } from './components/StatusBar/StatusBar'
+import { PetalCompanion } from './components/Companion/PetalCompanion'
 
 export default function App() {
   const [docs, setDocs] = useState<DocSummary[]>([])
@@ -16,6 +17,9 @@ export default function App() {
   // sidebar. Escape or a click outside the editor canvas restores it.
   const [focusMode, setFocusMode] = useState(false)
   const canvasRef = useRef<HTMLDivElement>(null)
+  // Monotonic counters the companion watches to react to writing + accepts.
+  const [editTick, setEditTick] = useState(0)
+  const [acceptTick, setAcceptTick] = useState(0)
 
   const { status, schedule, saveNow } = useAutoSave(currentDoc?.id ?? null)
   const {
@@ -116,6 +120,7 @@ export default function App() {
   const handleEditorChange = useCallback(
     (change: EditorChange) => {
       setWordCount(change.word_count)
+      setEditTick((n) => n + 1)
       if (currentDoc) {
         patchSummary(currentDoc.id, { word_count: change.word_count })
         schedule(change)
@@ -130,6 +135,7 @@ export default function App() {
   const handleAccept = useCallback(
     async (s: Suggestion) => {
       removeSuggestion(s.id)
+      setAcceptTick((n) => n + 1)
       try {
         await api.acceptSuggestion(s.id)
       } catch (err) {
@@ -238,6 +244,13 @@ export default function App() {
           )}
         </main>
       </div>
+
+      <PetalCompanion
+        wordCount={wordCount}
+        saveStatus={status}
+        editTick={editTick}
+        acceptTick={acceptTick}
+      />
     </div>
   )
 }