feat(ui): Mission Control Recent Sessions mit verschachtelten Handoffs

Neue Tabelle mission_control_sessions (Migration AddMissionControlSessions), befuellt vom
InteractiveLaunchSpecService bei Task-, Ad-hoc- und Handoff-Kacheln. Flyout im Mission-Control-Header
listet die letzten 14 Tage / 50 Sessions, Handoffs eingerueckt unter ihrer Ursprungs-Session, mit
Fortsetzen (--resume im gespeicherten cwd) und Brief anzeigen.

docs/explore-notes/conpty-sessions.md

@@ -124,6 +124,21 @@ with the same `IdentityKey` via `GetSessionHandoffLaunchSpec` → `BuildHandoffA
 tile, the new session id replaces `InteractiveSessionId`, so reopening the task resumes the
 handed-off session. The old transcript remains under `~/.claude/projects/`.
 
+## Recent sessions
+
+Every task, ad-hoc and handoff tile launch (only those — `paneId != null`) records its session in
+`mission_control_sessions` from inside `InteractiveLaunchSpecService`, which is where the session id
+is known. A handoff's predecessor comes from the brief's first line
+(`SessionHandoffMcpTools.ReadHandedOffFrom`), and it inherits the predecessor's title and task.
+The clock button in the Mission Control header opens a flyout (`RefreshRecentSessionsAsync`, last 14
+days / 50 rows, read straight from the DB). `NestHandoffs` groups each chain under its origin.
+- **Resume**: a task's *current* `InteractiveSessionId` reopens the task tile (deduped by TaskId).
+  Any other session gets a fresh ad-hoc tile via `GetResumeSessionLaunchSpec` → `BuildResumeAsync`
+  (`--resume <id>` in the recorded cwd, handoff hint included).
+- **Brief**: `ShellOpen.Path(brief.md)`, which opens the file in the default editor.
+- Not guarded: resuming a session that is still live in another ad-hoc tile, since panes don't
+  track their session id.
+
 ## List handler ("Let Claude handle it")
 
 `BuildForMergeHelperAsync`/`BuildForMergeHelperHandoffAsync` resolve `--permission-mode` via