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/Lobby.svelte

@@ -13,6 +13,7 @@
   import { badgeKind } from '../lib/unread';
   import { getLobby, setLobby } from '../lib/lobbycache';
   import { preloadGames } from '../lib/preload';
+  import { kickDictPreload } from '../lib/offline.svelte';
   import { gamePhase, groupGames, orderedSeats, scoreStanding, shouldBlink, type LobbyPhase } from '../lib/lobbysort';
   import type { AccountRef, GameView, Invitation } from '../lib/model';
   import { VARIANT_FLAG, VARIANT_RULES } from '../lib/variants';
@@ -51,7 +52,13 @@
       // Warm the cache for the ongoing games so opening one from the lobby is instant. The list
       // just loaded, so the connection is up; the call is non-blocking and re-running it on each
       // lobby refresh cheaply warms any newly appeared game (already-cached ones are skipped).
-      if (connection.online) void preloadGames(games);
+      if (connection.online) {
+        void preloadGames(games);
+        // Warm the offline dictionaries for an eligible install (PWA + email) so a later switch to
+        // offline mode already has the data; a no-op elsewhere, and cheap once cached. The first
+        // lobby entry surfaces a notice in place of the ad banner if a fetch fails.
+        kickDictPreload(app.profile, true);
+      }
     } catch (e) {
       handleError(e);
     } finally {

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);