Content-bearing notifications are still gated on the stale local privacy settings copy instead of Runtime Host policy

## Summary

Surfaced by the Sandbox/privacy documentation audit in #4800 (review by hqhq1025): the privacy authority moved to Runtime Host policy, but content-bearing notifications are still gated on the stale local settings copy. When a user enables incognito, notifications can keep exposing the session title and reply preview.

## Affected wiring

- `packages/runtime-host/src/.../notifications-ipc-main.ts` gates content-bearing notifications on the stale local privacy copy.
- `settings-ownership.ts` excludes privacy from the local settings patch, so the local copy is never the current authority.
- Runtime Host policy is the authority for privacy state.

Net effect: after enabling incognito, the run-ended notification path can still emit content-bearing text until some other mechanism refreshes or replaces the stale local copy.

## Suggested direction

Gate notification content on Runtime Host policy (the authority), or subscribe the notification path to policy changes so the stale local copy cannot be consulted.

Found during a documentation-accuracy audit; the implementation behavior was verified by the reviewer against the current tree but not reproduced end-to-end with a live incognito session in this issue.