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/screens/Profile.svelte

@@ -16,6 +16,7 @@
   import { gateway } from '../lib/gateway';
   import { insideTelegram, loginWidgetAvailable, requestTelegramLogin } from '../lib/telegram';
   import { insideVK } from '../lib/vk';
+  import { kickDictPreload } from '../lib/offline.svelte';
   import { startVKLink, vkWebLinkAvailable } from '../lib/vkid';
   import { t } from '../lib/i18n/index.svelte';
   import {
@@ -158,6 +159,9 @@
         notificationsInAppOnly,
         variantPreferences: variantPrefs,
       });
+      // A variant-preference change may enable a variant whose dictionary is not yet cached; warm
+      // it in the background for offline readiness (quietly — no in-lobby notice for a top-up).
+      kickDictPreload(app.profile, false);
       showToast(t('profile.saved'));
     } catch (e) {
       handleError(e);