Grow the companion, fix idle fallback, add update banner

Companion: bump the corner mascot ~12% (128→144) and make animation
resolution robust — fall back to the idle clip when a mood has no clip of
its own, and pin the always-asleep cat to one pose so its Lottie never
reloads. This stops a bare emoji from replacing the cute companion on idle.

Update notifications: serve a build id at /api/version (a hash of the
embedded dist/index.html, which changes on every frontend deploy). The
client records its load-time id, polls every 90s (and on tab focus), and
floats a Mandarin-first "new version available" banner offering a refresh
when the id changes.

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

web/src/components/Companion/PetalCompanion.tsx

@@ -44,10 +44,20 @@ export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick }:
   // dozes them, keep their normal idle pose instead of a sleepy face. Only a
   // mascot with a real sleep animation (the always-asleep cat) shows the zzz.
   const hasSleepClip = Boolean(companion.animations.sleeping)
-  const renderMood: Mood =
-    mood === 'sleeping' && !companion.alwaysAsleep && !hasSleepClip ? 'idle' : mood
+  // An always-asleep mascot (the cat) stays pinned to one pose so its Lottie
+  // never reloads as the engine flips moods underneath it.
+  const renderMood: Mood = companion.alwaysAsleep
+    ? 'idle'
+    : mood === 'sleeping' && !hasSleepClip
+      ? 'idle'
+      : mood
   const napping = companion.alwaysAsleep || (mood === 'sleeping' && hasSleepClip)
 
+  // Never swap the cute companion for a bare emoji on an idle nap: fall back to
+  // the idle animation when a mood has no clip of its own, and only reach for
+  // the emoji if the companion ships no animations at all.
+  const animationData = companion.animations[renderMood] ?? companion.animations.idle
+
   function choose(id: string) {
     setCompanionId(id)
     try {
@@ -153,8 +163,8 @@ export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick }:
         aria-label="Choose a companion"
         className={`petal-companion pointer-events-auto select-none ${napping ? 'petal-companion-sleep' : ''}`}
         style={{
-          width: 128,
-          height: 128,
+          width: 144,
+          height: 144,
           padding: 0,
           borderRadius: 'var(--radius-pill)',
           background: 'var(--color-surface-alt)',
@@ -167,9 +177,9 @@ export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick }:
       >
         <LottiePlayer
           key={companion.id}
-          animationData={companion.animations[renderMood]}
-          className="h-28 w-28"
-          fallback={<span style={{ fontSize: 64, lineHeight: 1 }}>{MOOD_EMOJI[renderMood]}</span>}
+          animationData={animationData}
+          className="h-32 w-32"
+          fallback={<span style={{ fontSize: 72, lineHeight: 1 }}>{MOOD_EMOJI[renderMood]}</span>}
         />
         {napping && (
           <span className="petal-zzz absolute" aria-hidden style={{ color: 'var(--color-muted)' }}>