feat(maestro): stamp the daemon with its build commit

`GET /api/info` now carries `build` (commit hash, commit date, dirty flag)
and `instance`, a fresh uuid per daemon process. Together they let a client
name the release it is talking to and, after losing its socket, tell an
upgrade from a plain restart from a network blip.

The stamp comes from `maestro-daemon/build.rs`, which reads the git checkout
it compiles in. The Nix build has no `.git` in the crane-filtered source, so
`flake.nix` passes the flake's own revision and last-modified date through
`MAESTRO_BUILD_*` instead. Neither available leaves the fields empty.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/src/types.ts

@@ -86,6 +86,24 @@ export interface DaemonInfo {
   home_dir?: string;
   /** Command presets (claude/opencode/zsh + custom), config-resolved. */
   presets: SpawnPreset[];
+  /** Which commit the daemon was built from. Absent on older daemons. */
+  build?: BuildInfo;
+  /** Identity of the daemon *process*, regenerated on every start — a changed
+   * value across a reconnect means the daemon restarted. Absent on older
+   * daemons, which the restart flow treats as "cannot tell". */
+  instance?: string;
+}
+
+/** Build provenance of the running daemon: what the status indicator names in
+ * its tooltip, and what tells an upgrade apart from a plain restart. Every
+ * field is empty when the binary was built outside a git checkout. */
+export interface BuildInfo {
+  /** Abbreviated commit hash. */
+  commit: string;
+  /** Commit date, RFC 3339. */
+  commit_date: string;
+  /** Whether the tree had uncommitted changes at build time. */
+  dirty: boolean;
 }
 
 /** One deduplicated recent working dir for the spawn form's recents picker