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
