fix(app): resync session stream after iOS PWA returns from background

[ysm-dev]

Issue for this PR

Closes #17769

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When the web app runs as a PWA on iOS and is backgrounded, Safari suspends JS and quietly closes the SSE connection. On resume the existing visibility heuristic skipped reconnect because the last event timestamp was within the heartbeat window right before suspension, so the session UI stayed frozen until the user manually refreshed.

Changes:

• `global-sdk.tsx`: track the `hidden` flag explicitly; on `visibilitychange` to visible (and `pageshow` with `event.persisted` for bfcache), force-reconnect with a 1s debounce. Detect successful reconnects (`server.connected` arriving while already connected) and emit a new `event.reconnect`.
• `session.tsx`: subscribe to `event.reconnect` and force-resync the active session messages. The directory bootstrap re-fetches the session list but not message bodies, so events arriving during the gap would otherwise be lost.
• `sync.tsx`: extend `runInflight` so a `force: true` call still re-runs after a non-force task currently in flight (queues after success or failure). Wired into `session.sync()`.
• `sync-optimistic.test.ts`: tests for the new `runInflight` behavior.

How did you verify your code works?

Manual: installed the web app to home screen on iOS, started a streaming session, switched apps for ~30s, returned — the stream resumes and the session catches up without a refresh.

Automated:

• `bun test src/context/sync-optimistic.test.ts` from `packages/app` (7 pass)
• `bun typecheck` from `packages/app`

Screenshots / recordings

N/A — no UI surface changed.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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