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/hooks/useVersionWatch.ts

@@ -0,0 +1,52 @@
+import { useEffect, useRef, useState } from 'react'
+import { api } from '../api/client'
+
+// How often to ask the server whether a newer frontend has shipped. Gentle —
+// a deploy is rare, and the check is a tiny no-store GET.
+const POLL_MS = 90_000
+
+// useVersionWatch records the build id the app loaded with, then quietly polls
+// /api/version. When the server reports a different id, a new version has been
+// deployed and `updateAvailable` flips true (and stays true) so the UI can
+// offer a refresh. Network blips are ignored — it only ever reacts to a real,
+// confirmed change. Returns false until the baseline is established.
+export function useVersionWatch(): boolean {
+  const [updateAvailable, setUpdateAvailable] = useState(false)
+  // The version we're currently running. Null until the first successful fetch.
+  const baseline = useRef<string | null>(null)
+
+  useEffect(() => {
+    let active = true
+
+    const check = async () => {
+      try {
+        const { version } = await api.version()
+        if (!active || !version) return
+        if (baseline.current === null) {
+          baseline.current = version // first read: this is "us"
+        } else if (version !== baseline.current) {
+          setUpdateAvailable(true)
+        }
+      } catch {
+        /* offline / server bounce — try again next tick, never alarm the user */
+      }
+    }
+
+    check()
+    const id = setInterval(check, POLL_MS)
+    // Re-check the moment she returns to the tab, so a deploy that happened while
+    // she was away surfaces right away instead of up to POLL_MS later.
+    const onVisible = () => {
+      if (document.visibilityState === 'visible') check()
+    }
+    document.addEventListener('visibilitychange', onVisible)
+
+    return () => {
+      active = false
+      clearInterval(id)
+      document.removeEventListener('visibilitychange', onVisible)
+    }
+  }, [])
+
+  return updateAvailable
+}