Persist Daybreak preferences in thread metadata (#42854)

## Why

Clients need a per-thread Daybreak toggle that survives restarts and can be
restored on resume without changing the access program of an active or future
turn.

## What changed

- Add experimental `daybreakEnabled` support to `thread/metadata/update` and
  expose the saved value on thread responses.
- Store the preference in SQLite, including for threads without a first turn,
  and preserve it through reads, resumes, reconciliation, and restarts.
- Copy the preference when forking a thread while keeping subsequent updates
  independent.
- Keep `daybreakEnabled` separate from the per-turn `cyberAccessProgram` field;
  app-server does not derive one from the other.

## Testing

- Cover persistence across restarts, cold reads, reconciliation, and forks.
- Verify metadata updates do not alter the access program of active or later
  turns.

GitOrigin-RevId: bcf987a9fcd7b0ac8a88b1c8f0df06b33ed8ad6e

codex-rs/analytics/src/client_tests.rs

@@ -601,6 +601,7 @@ fn sample_thread(thread_id: &str) -> Thread {
         section: None,
         section_entered_at: None,
         project_id: None,
+        daybreak_enabled: None,
         history_mode: Default::default(),
         model_provider: "openai".to_string(),
         model: None,