[Bug]: Left sidebar resurrects stale/deleted sessions #129

What happened?

The left sidebar sometimes resurrects sessions that were removed — either stale entries lingering after cleanup, or sessions that were explicitly deleted showing up again on the next render/refresh.

Expected: deleted sessions stay deleted; stale ghost/root entries do not re-materialize after cleanup; the sidebar matches the truth of the sessions store + on-disk ghost entries with no zombie rows.

Steps to reproduce

1. Open Tempest with an existing project that has sessions.
2. Delete a session from the sidebar (context menu → remove).
3. Trigger a sidebar re-render (switch mode, reopen project, or restart the app).
4. The removed session reappears in the list.

Also reproducible with worktree ghost entries that should have been cleaned up.

Tempest version

0.1.21

Operating system

Windows 11

OS version

Windows 11 Home Single Language 10.0.26200

Relevant logs or screenshots

Likely culprits to audit while triaging:

• store/sessions ghost/root persistence: getRootSessionsForProject, getBranchSessions, getWorktreeAgentSession.
• Merge logic in LeftSidebar.tsx combining live sessions with ghost entries (sbRows, filtering by liveIds).
• Any delete path that removes the live session but leaves the persisted ghost, or vice versa.

Before submitting

• I searched existing issues and this hasn't been reported yet
• I'm on the latest version, or I've noted the version above