feat(raft-apply-decoupling): build apply_committed_entry single dispatch seam (task 2.2)

Add apply_committed_entry(persist_t*, wal_type, lsn, payload, len) in
persist.c/persist.h as the single seam that turns a committed WAL
entry into an in-memory mutation plus its post-mutation notification
hook, covering job submit, job-state facts, queue control, and
worker control. Job-state facts route through 2.1's guard-only
apply_job_update_transition() core and fire a generic
HOOK_DETAIL_JOB_UPDATE, not per-type hooks — the wire format
(wal_jobstate_t {jobid, state}) cannot supply what the type-specific
cores/hooks require. This is a real, documented deviation from
design.md's per-type dispatch wording; tasks.md's Implementation
Notes flags it as unresolved and blocking for whoever wires this
into a live path (4.1/6.2/6.3).

Not yet wired into any live call site (replay wiring is 2.3).

src/controller/meson.build

@@ -158,6 +158,7 @@ controller_unit_test_src = [
   'testsuite/snapdiff.c',
   'testsuite/test_persist_snapshot_entities.c',
   'testsuite/test_apply_seam.c',
+  'testsuite/test_apply_committed_entry.c',
   'ctrlstatus.c',
   'commit.c',
   'job.c',