feat(ha-entity-snapshots): add spec + task 1.1 test fixture

Adds the ha-entity-snapshots Kiro spec (requirements, design, research,
tasks) for task 5.10a / raft-ha-core-safety: making the HA checkpoint an
actually-restorable copy of committed job/queue state instead of a
position-only sentinel, closing the residual chaotic-soak divergence gap.

Task 1.1 (foundation): reusable test fixture snapent_make/snapent_teardown
in a new test_persist_snapshot_entities.c, seeding N jobs (varying state)
and M queues (varying status) into a real persist_t+cluster_t for later
write/load/rotation-guard tests to build on. Build clean; new suite 1/1;
regression spot-checks (test_persist_hooks 19/19, test_commit_barrier_reply
22/22) clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JDYFbrgyDHbvNYcxApKhrX

src/controller/meson.build

@@ -151,6 +151,7 @@ controller_unit_test_src = [
   'testsuite/waldump.c',
   'testsuite/test_walcompare.c',
   'testsuite/walcompare.c',
+  'testsuite/test_persist_snapshot_entities.c',
   'ctrlstatus.c',
   'commit.c',
   'job.c',