feat(config-upgrade-snapshot): restore host admin-state frame safely (create-if-missing)

Adds restore_host_state(cluster_t*, const char*, uint32_t admin_status)
to worker.c: OR's admin bits into an existing worker's status on hit;
on miss, creates a minimal XCE_WORKER_UNAVAIL placeholder via
makeWorker (mirroring the lost_and_found sentinel host precedent),
with a valid non-NULL hostattrs_t so the host's later real join routes
through rejoin_worker (not init_worker) and preserves the restored
admin status. Idempotent under retry (find first, create only if
missing). Standalone -- not yet wired into load_snapshot (task 4).

Requirements: 1.10, 1.11, 5.8

src/controller/meson.build

@@ -168,6 +168,7 @@ controller_unit_test_src = [
   'testsuite/test_job_array_apply.c',
   'testsuite/test_job_array_fence.c',
   'testsuite/test_job_array_replay_fence.c',
+  'testsuite/test_upgrade_snapshot_restore.c',
   'ctrlstatus.c',
   'commit.c',
   'job.c',