feat(offline): background-preload dictionaries for offline readiness

An installed PWA (standalone web + confirmed email) warms the dictionaries
for the player's enabled variants while online — on lobby entry and on a
variant-preference change — using the per-variant version the profile now
advertises, so a later switch to offline mode already has the data.

- dict/preload.ts: pure preloadDicts (retry + linear backoff, honours the
  session dictionary miss-breaker); node-tested.
- dict/preloadrun.ts: lazy browser orchestration (real getDawg), imported
  dynamically so the loader and move generator stay out of the main bundle.
- offline.svelte.ts: kickDictPreload, gated by the pure, tested
  offlinePreloadEligible, plus the reactive first-lobby preload warning.
- Header shows a poor-connection notice in the ad-banner slot on a
  first-lobby preload failure (offline.preloadWarning, en/ru).
- App-entry bundle budget 112->113 for the irreducible main-side wiring
  (documented in bundle-size.mjs); the heavy parts remain lazy chunks.

Docs: ARCHITECTURE offline-mode + dict-preload mechanism.

ui/src/lib/offline.svelte.ts

@@ -3,7 +3,11 @@
 // Settings toggle is the source of truth), distinct from connection.svelte.ts's transient
 // gateway-reachability signal. The pure persistence + readiness logic lives in offline.ts.
 
-import { loadOfflinePref, saveOfflinePref } from './offline';
+import { loadOfflinePref, saveOfflinePref, offlinePreloadEligible } from './offline';
+import { isStandalone } from './pwa';
+import { insideTelegram } from './telegram';
+import { insideVK } from './vk';
+import type { Profile } from './model';
 
 // Not named `state` (a svelte-check hazard: `$state` would then read as a store subscription).
 let active = $state(loadOfflinePref());
@@ -21,3 +25,55 @@ export function setOfflineMode(on: boolean): void {
   active = on;
   saveOfflinePref(on);
 }
+
+// The dict-preload warning: true when a first-lobby background preload could not fetch every
+// enabled variant's dictionary (typically a poor connection), so offline mode may be incomplete.
+// The lobby shows a notice in place of the ad banner while it holds.
+let preloadWarn = $state(false);
+
+/** dictPreloadWarning exposes the reactive preload-failure flag; read it in markup / $derived. */
+export const dictPreloadWarning = {
+  /** active is true while a first-lobby dictionary preload has left a variant unavailable. */
+  get active(): boolean {
+    return preloadWarn;
+  },
+};
+
+/** setDictPreloadWarning raises or clears the in-lobby preload-failure notice. */
+export function setDictPreloadWarning(on: boolean): void {
+  preloadWarn = on;
+}
+
+// A preload runs at most once at a time; it finishes before a fresh trigger (a repeated lobby
+// mount or a variant-preference change) can start another. Module-scoped so mounts do not stack.
+let preloadInFlight = false;
+
+/**
+ * kickDictPreload starts a background preload of the enabled variants' dictionaries for an
+ * offline-capable install (a standalone web PWA with a confirmed email) while online, so a later
+ * switch to offline mode already has the data. It is a no-op in a Telegram/VK mini-app, in a plain
+ * browser tab, without a confirmed email, while offline, or when a preload is already running;
+ * getDawg's caching makes a repeat run cheap. When warnOnFail is set (the first lobby entry), a
+ * fetch failure raises the in-lobby notice, and a later successful run clears it. The dict loader
+ * and generator are imported dynamically, so neither is pulled into the main bundle.
+ */
+export function kickDictPreload(prof: Profile | null, warnOnFail = false): void {
+  if (preloadInFlight || !prof) return;
+  const eligible = offlinePreloadEligible({
+    hasEmail: !!prof.email,
+    standalone: isStandalone(),
+    inTelegram: insideTelegram(),
+    inVK: insideVK(),
+    online: typeof navigator === 'undefined' || navigator.onLine !== false,
+  });
+  if (!eligible) return;
+  preloadInFlight = true;
+  void import('./dict/preloadrun')
+    .then((m) => m.runPreload(prof, warnOnFail))
+    .catch(() => {
+      /* best-effort warmup — a failed dynamic import just leaves offline data unprimed */
+    })
+    .finally(() => {
+      preloadInFlight = false;
+    });
+}