Fix goal-first live threads missing from thread/list

[etraut-openai]

Fixes #28263.

Why

When a thread starts with /goal, the goal extension can update SQLite goal state before the thread has any user-turn rollout items. thread/list discovers and repairs listing metadata from persisted rollout items, so a goal-first live thread could be absent from app-server listings after restart even though the goal itself existed.

This regressed when goal handling moved out of core: the core path wrote the goal update into the live thread rollout, while the extension-backed app-server path only updated goal state and emitted the live notification.

What

• Add GoalSetOutcome::thread_goal_updated_item() so the goal extension owns the canonical ThreadGoalUpdated rollout item shape.
• When app-server sets a goal on an active live thread, append that rollout item to ThreadStore so listing repair can recover the thread preview.
• Add an app-server regression test that starts a live thread with thread/goal/set and verifies it appears in thread/list.

Verification

• env -u CODEX_SQLITE_HOME just test -p codex-app-server goal_first_live_thread_appears_in_thread_list