fix(maestro): mirror last_focused_at in the web session type

The daemon ships the field (#145) but web/src/types.ts is a hand-kept
mirror of the protocol crate, so it did not know about it. #149 sorts the
command bar's empty query by it.

web/src/types.ts

@@ -50,6 +50,12 @@ export interface Session {
    * create one. `base_repo` is the repository's main checkout, which is what
    * the session tree groups by (#99). */
   worktree?: SessionWorktree | null;
+  /** Wall-clock of when this session last became the pane a client was showing
+   * (#145) — stamped by both `POST /api/sessions/:id/focus` and opening
+   * `/api/attach/:id`. Absent until the session has been focused once, which is
+   * how the command bar's empty query sorts a never-focused session after every
+   * session that has one (`docs/COMMAND-BAR.md`). */
+  last_focused_at?: IsoTimestamp | null;
 }
 
 /** A session's daemon-created worktree (`SessionWorktree` on the wire). */