fix(frontend): refresh guild tokens on mount to avoid stale-token 401

Guild access tokens (15-min TTL) are persisted in localStorage but were
never refreshed on page (re)load - only the center token was. After the
TTL elapsed, GET /channels failed with 401 ('Failed to load channels').
Re-issue guild tokens via refreshGuilds() on mount and reload channels
when the guild token changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/ChatPage.tsx

@@ -42,6 +42,14 @@ export default function ChatPage() {
     if (!selectedGuildId && guilds.length) setSelectedGuildId(guilds[0].nodeId)
   }, [guilds, selectedGuildId])
 
+  // Guild access tokens have a short TTL and are persisted in localStorage.
+  // On (re)load they may be expired, so re-issue fresh ones from Center
+  // before any guild API call. refreshGuilds also refreshes the center token.
+  useEffect(() => {
+    refreshGuilds().catch(() => {})
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [])
+
   const guild = useMemo(() => guilds.find((g) => g.nodeId === selectedGuildId) ?? null, [guilds, selectedGuildId])
   const guildToken = useMemo(
     () => (session?.guildAccessTokens ?? []).find((x) => x.guildNodeId === selectedGuildId)?.token ?? '',
@@ -196,7 +204,7 @@ export default function ChatPage() {
     void loadChannels()
     setMessages([])
     setSelectedChannelId('')
-  }, [selectedGuildId, guildDbId])
+  }, [selectedGuildId, guildDbId, guildToken])
 
   useEffect(() => {
     void pullMessages()