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/lib/app.svelte.ts

@@ -304,7 +304,9 @@ export function handleError(err: unknown): void {
     void enterBlocked();
     return;
   }
-  if (isConnectionCode(code) || !connection.online) return;
+  // A blocked call in offline mode ('offline', the transport kill switch) is expected, not an error
+  // to surface — the offline chrome already signals the state; never a red toast.
+  if (isConnectionCode(code) || code === 'offline' || !connection.online) return;
   haptic('error');
   showToast(t(code ? errorKey(code) : 'error.generic'), 'error');
 }
@@ -585,18 +587,28 @@ function promptOfflineChoice(): Promise<boolean> {
  * cold-start dialog) is left as the player's choice. These are passive OS events — no polling, no
  * battery cost. Web-only and skipped in the mock (the e2e drives connectivity directly).
  */
+// tryReturnOnline is fired from the online event while in auto-offline: the interface being back does
+// not mean the gateway is reachable yet (DNS/routing settle for a moment after flight mode), so it
+// re-checks a few times with backoff before returning online, stopping if the player takes over the
+// state meanwhile. This bounded retry is what actually gets the app back online after flight mode off.
+async function tryReturnOnline(): Promise<void> {
+  for (let attempt = 0; attempt < 4; attempt++) {
+    if (!offlineMode.active || !offlineMode.auto) return;
+    if (await checkReachable(BOOT_REACHABILITY_TIMEOUT_MS)) {
+      if (offlineMode.active && offlineMode.auto) setOfflineMode(false);
+      return;
+    }
+    await new Promise((r) => setTimeout(r, 600 * (attempt + 1)));
+  }
+}
+
 export function initNetworkReactivity(): void {
   if (typeof window === 'undefined' || import.meta.env.MODE === 'mock') return;
   window.addEventListener('offline', () => {
     if (!offlineMode.active) setOfflineMode(true, false); // auto (session) — self-heals below
   });
   window.addEventListener('online', () => {
-    if (offlineMode.active && offlineMode.auto) {
-      void checkReachable(BOOT_REACHABILITY_TIMEOUT_MS).then((reachable) => {
-        // Re-read the flags — the player may have chosen offline meanwhile — before returning online.
-        if (reachable && offlineMode.active && offlineMode.auto) setOfflineMode(false);
-      });
-    }
+    if (offlineMode.active && offlineMode.auto) void tryReturnOnline();
   });
 }