feat: P2-4 wire repl_broadcast into persist_wal_async/sync_append; last_replicated_crc

- Move repl.h from controller/ to include/ (shared header) to break
  persist.h ↔ repl.h circular include
- Extract wal_entry_hdr_t + wal_entry_type into include/wal_types.h so
  repl.h can include only what it needs without pulling in all of persist.h
- Add replicator_t repl field to persist_t (embedded by value, P2-4)
- Wire repl_init/repl_fini into persist_init/persist_fini lifecycle
- Wire repl_broadcast into persist_wal_async after each WAL write;
  last_replicated_crc updated here (not in persist_write_checkpoint_marker)
- Wire repl_wait_ack into persist_wal_sync_append; returns 0 on local
  WAL success; sync_rc_out carries -ENODEV/-ETIMEDOUT for degraded mode
- Add 4 TDD tests in test_persist_repl.c: structural repl field check,
  async no-standbys succeeds, sync degraded mode rc, checkpoint CRC invariant

src/controller/testsuite/controller_test.c

@@ -25,6 +25,7 @@ extern void test_ha_redirect(void);
 extern void test_p1_integration(void);
 extern void test_repl_unit(void);
 extern void test_repl_apply(void);
+extern void test_persist_repl(void);
 
 void setUp(void) { return; }
 
@@ -119,6 +120,7 @@ int main(int argc, char* argv[])
     TEST(test_p1_integration);
     TEST(test_repl_unit);
     TEST(test_repl_apply);
+    TEST(test_persist_repl);
 
     return UNITY_END();
 }