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.ts

@@ -41,3 +41,20 @@ export function offlineReady(enabled: readonly Variant[], hasDict: (v: Variant)
 export function missingDicts(enabled: readonly Variant[], hasDict: (v: Variant) => boolean): Variant[] {
   return enabled.filter((v) => !hasDict(v));
 }
+
+/**
+ * offlinePreloadEligible reports whether a background dictionary preload should run in this
+ * context: an installed standalone web PWA (not a Telegram/VK mini-app, not a plain browser tab)
+ * with a confirmed email, currently online. Elsewhere the preload is wasted bandwidth — the context
+ * has no offline mode to prepare for — so kickDictPreload skips it. Mirrors the Settings offline
+ * toggle's eligibility so the two never disagree.
+ */
+export function offlinePreloadEligible(opts: {
+  hasEmail: boolean;
+  standalone: boolean;
+  inTelegram: boolean;
+  inVK: boolean;
+  online: boolean;
+}): boolean {
+  return opts.hasEmail && opts.standalone && !opts.inTelegram && !opts.inVK && opts.online;
+}