agent v0.36.0: guest boot-id on /disks (deterministic guest-reboot recreate)

GET /disks emits guest_boot_id = <host-btime>-<guest-init-starttime>: changes on
every guest/host boot, stable across controller-only restarts. The controller
persists it + deterministically recreates drive-backed apps on change (replaces
the timed state-sample). Non-hollow parser test + companion.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/localapi/disks_test.go

@@ -422,6 +422,7 @@ func (f *fakeGuestAttacher) AttachDrive(_ context.Context, _ int, where string)
 	return StablePathForRaw(where), nil
 }
 func (f *fakeGuestAttacher) GuestSeesMount(_ context.Context, _ int, _ string) bool { return true }
+func (f *fakeGuestAttacher) GuestBootID(_ context.Context, _ int) string             { return "boot-1" }
 func (f *fakeGuestAttacher) attachDriveCount() int {
 	f.mu.Lock()
 	defer f.mu.Unlock()