test: P0-G end-to-end smoke tests — WAL, checkpoint, hooks, GC, Cap'n Proto (P0-15a-e)

Add 5 E2E integration test files that cross sub-phase boundaries:

- test_e2e_wal.c (P0-15a): WAL write+read-back (entry count), torn-write
  recovery via ftruncate + persist_recover(), chained-CRC corruption stops
  replay at last valid entry.

- test_e2e_checkpoint.c (P0-15b): 20-entry WAL + checkpoint + 10 post-
  checkpoint entries + recover asserts current_lsn >= 30 and checkpoint_lsn
  > 0; WAL trim after two checkpoints; snap_keep_n rotation with 4 rounds.

- test_e2e_hooks.c (P0-15c): persist_job_hook_fun(HOOK_DETAIL_JOB_NEW)
  writes WAL_JOB_SUBMIT entry; persist_worker_hook_fun(HOOK_DETAIL_WORKER_JOIN)
  writes WAL_WORKER_CTRL; 3-call sequence preserves monotone LSN order and
  verifies header LSN fields on disk.

- test_e2e_gc.c (P0-15d): running job retained; expired finished job not
  retained; JOB_STAT_TRANSIENT times out; expired unavailable worker not
  retained; checkpoint-after-WAL integration smoke.

- test_e2e_capnp.c (P0-15e): persist_config_t → capnp_persist_cfg_t 8-field
  round-trip; capnp_snap_hdr_t field values and struct size (48 bytes);
  capnp_repl_envelope_t fields including WAL_CRC_NONE sentinel.

Total: 89 tests, 0 failures (was 72 before this commit).

src/controller/meson.build

@@ -77,6 +77,11 @@ controller_unit_test_src = [
   'testsuite/test_persist_hooks.c',
   'testsuite/test_gc_retention.c',
   'testsuite/test_cluster_persist.c',
+  'testsuite/test_e2e_wal.c',
+  'testsuite/test_e2e_checkpoint.c',
+  'testsuite/test_e2e_hooks.c',
+  'testsuite/test_e2e_gc.c',
+  'testsuite/test_e2e_capnp.c',
   'persist.c',
 ]