feat(ui): explicit offline state inside an online game (+ offline word check)

When an online game loses the connection the game screen now says so and freezes
instead of silently greying out: a "connection lost" banner appears and the rack,
the move controls, the add-friend/block controls and the chat/dictionary entry all
disable (a started move stays a draft, committed by the player on reconnect). It is
driven off the net-state machine (netState.offline), so it also covers the
Telegram/VK mini-apps, where a lost connection was previously mute in-game.

If the player is already in the dictionary when the drop happens, the word check
falls back to the game's pinned on-device dictionary (exact when that dawg is
cached; "unavailable offline" otherwise) and the network-only complaint + external
look-up hide. Chat, when already open, keeps its existing read-only degrade
(send/nudge disable). New pure helper localWordCheck is unit-tested; the in-game
gating gets an e2e.

ui/src/lib/dict/check.ts

@@ -0,0 +1,26 @@
+// Offline word-check fallback for an online game. An online game's dictionary check normally goes to
+// the gateway (game.check_word); while disconnected that call fails, so the check falls back to the
+// game's own pinned dictionary read locally. Using the game's pinned (variant, version) means the
+// answer matches the server's — no divergence — as long as that dawg is available on-device; if it
+// is not cached/bundled offline, the check is simply unavailable (null). The membership test mirrors
+// the local engine's dictionaryHas (encode to alphabet indices, then Dawg.indexOf).
+
+import { getDawg } from './loader';
+import { indexForLetter } from '../alphabet';
+import type { Variant } from '../model';
+
+/**
+ * localWordCheck reports whether word is in the (variant, version) dictionary using the on-device
+ * dawg, or null when that dawg cannot be obtained (offline and neither cached nor bundled). word
+ * must already be sanitised to the variant's alphabet (as the check panel does).
+ */
+export async function localWordCheck(
+  variant: Variant,
+  version: string,
+  word: string,
+): Promise<boolean | null> {
+  const dawg = await getDawg(variant, version);
+  if (!dawg) return null;
+  const idx = Array.from(word, (ch) => indexForLetter(variant, ch));
+  return dawg.indexOf(idx) >= 0;
+}