fix(offline): return online after flight-mode off; gate online-game actions offline

Two mid-session issues found on the contour:
- Auto-offline did not return to online after the network came back: a single
  reachability check right after the 'online' event failed (the interface is up
  before the gateway is actually reachable again). Retry a few times with backoff
  (tryReturnOnline) — that is what actually gets the app back online.
- An online game viewed while offline (flight mode on) still enabled its network
  actions, so they hit the kill switch and raised 'something went wrong' toasts.
  Gate them: netReady = isLocalGame || (connection.online && !offlineMode.active)
  — a local game stays fully usable; an online game's make/exchange/hint/resign
  disable while offline and re-enable when back. Also suppress the 'offline' code
  in handleError (a blocked call in offline mode is expected, not a toast).

ui/src/game/Game.svelte

@@ -13,6 +13,7 @@
   import { navigate } from '../lib/router.svelte';
   import { app, handleError, showToast, markChatRead, seedChatUnread } from '../lib/app.svelte';
   import { connection } from '../lib/connection.svelte';
+  import { offlineMode } from '../lib/offline.svelte';
   import { GatewayError } from '../lib/client';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
   import type { EvalResult, MoveRecord, MoveResult, StateView, Tile } from '../lib/model';
@@ -52,6 +53,11 @@
   // screen calls the game-loop methods (state/history/submit/pass/exchange/resign/hint/evaluate/
   // draft) through it, so the same UI drives a local vs_ai game and an online one alike.
   const source = $derived(gameSource(id));
+  // A local (offline) game plays entirely on-device, so it is always ready; an online game needs a
+  // live connection — and offline mode's kill switch refuses its calls — so its network actions are
+  // disabled while disconnected or in offline mode (which also stops the "something went wrong"
+  // toasts a blocked call would otherwise raise).
+  const netReady = $derived(isLocalGameId(id) || (connection.online && !offlineMode.active));
   // Unsubscribes from a local game's robot-reply events (offline only; null for a network game).
   let localUnsub: (() => void) | null = null;
 
@@ -1481,19 +1487,19 @@
       />
     </div>
     {#if !gameOver && placement.pending.length > 0 && !recallOverRack}
-      <button class="make" onclick={commit} disabled={busy || !isMyTurn || !connection.online || !preview?.legal} aria-label={t('game.makeMove')}>✅</button>
+      <button class="make" onclick={commit} disabled={busy || !isMyTurn || !netReady || !preview?.legal} aria-label={t('game.makeMove')}>✅</button>
     {/if}
   </div>
 {/snippet}
 
 {#snippet controlButtons()}
-  <button class="tab" disabled={busy || !isMyTurn || !connection.online} onclick={openExchange}>
+  <button class="tab" disabled={busy || !isMyTurn || !netReady} onclick={openExchange}>
     <span class="sq" data-coach="game-turn">🔄</span><span class="lbl">{t('game.draw')}</span>
   </button>
   <TapConfirm
     triggerClass="tab"
     label={t('game.hint')}
-    disabled={busy || !isMyTurn || !connection.online || hintCount <= 0}
+    disabled={busy || !isMyTurn || !netReady || hintCount <= 0}
     onconfirm={doHint}
   >
     <span class="sq" data-coach="game-hints">🛟{#if hintCount > 0}<span class="badge">{hintCount}</span>{/if}</span>
@@ -1551,7 +1557,7 @@
   <Modal title={t('game.confirmResign')} onclose={() => (resignOpen = false)}>
     <div class="confirm-row">
       <button class="cancel" onclick={() => (resignOpen = false)}>{t('common.cancel')}</button>
-      <button class="danger" onclick={doResign} disabled={!connection.online}>{t('game.dropGame')}</button>
+      <button class="danger" onclick={doResign} disabled={!netReady}>{t('game.dropGame')}</button>
     </div>
   </Modal>
 {/if}
@@ -1563,7 +1569,7 @@
         <button
           class="confirm"
           onclick={() => { exportOpen = false; void exportArtifact('png'); }}
-          disabled={!connection.online}
+          disabled={!netReady}
         >
           {t('game.exportImageOpt')}
         </button>
@@ -1571,7 +1577,7 @@
       <button
         class={exportImageAvailable ? 'export-alt' : 'confirm'}
         onclick={() => { exportOpen = false; void exportArtifact('gcg'); }}
-        disabled={!connection.online}
+        disabled={!netReady}
       >
         {t('game.exportGcgOpt')}
       </button>