fix(offline): AI comms hub opens straight to the Dictionary, not via Chat

For an honest-AI (vs_ai) game the comms hub relied on a post-mount $effect to
switch from the Chat tab to the Dictionary, so ChatScreen mounted for a beat
and fired its chat/state fetch over the network. Online that was a wasted
call; offline it threw and raised a 'something went wrong' toast on entering
the word-check form (the check itself already worked). Start the comms hub on
the Dictionary tab immediately for a vs_ai game, so ChatScreen never mounts.

ui/src/game/CommsHub.svelte

@@ -21,8 +21,11 @@
   // Seeded once from the entry route's tab, then owned locally. The effect keeps the tab valid:
   // an AI game has only the Dictionary; a finished non-AI game has only Chat (a stale Dictionary
   // deep-link falls back to Chat).
+  // An honest-AI game has only the Dictionary, so start there regardless of the entry route — this
+  // keeps ChatScreen (which fetches chat over the network) from mounting even for a beat, which would
+  // otherwise raise an error toast in offline mode.
   // svelte-ignore state_referenced_locally
-  let tab = $state<CommsTab>(initialTab);
+  let tab = $state<CommsTab>(vsAi ? 'dictionary' : initialTab);
   $effect(() => {
     if (vsAi) tab = 'dictionary';
     else if (tab === 'dictionary' && !active) tab = 'chat';