feat: persistence hook functions wired to WAL write on AFTER_EVENT (P0-6)

Implements persist_job_hook_fun, persist_queue_hook_fun, and
persist_worker_hook_fun — AFTER_EVENT hooks that write WAL entries
whenever state mutations occur in the controller.

- detail_to_wal_type() maps all 15 HOOK_DETAIL_* values to WAL types;
  unknown details return 0 and are silently skipped
- HOOK_DETAIL_JOB_NEW uses the sync replication path (WAL_JOB_SUBMIT);
  all others use persist_wal_async
- P0 payload: 4-byte detail value; full Cap'n Proto serialization in Task 15
- Hook signature matches hook_fn_t exactly:
  int fn(int type, int situation, int detail, void* cls, va_list ap)
- Added <stdarg.h> to persist.h for va_list; added hook.h and
  xce/cluster_def.h includes to persist.c
- 18 new unit tests in test_persist_hooks.c covering all 15 detail→WAL
  mappings, skip-on-unknown, and sequential LSN advancement

src/controller/meson.build

@@ -74,6 +74,7 @@ controller_unit_test_src = [
   'testsuite/test_persist_checkpoint.c',
   'testsuite/test_persist_recovery.c',
   'testsuite/test_hooks.c',
+  'testsuite/test_persist_hooks.c',
   'persist.c',
 ]