test(ha-config-bootstrap): RED phase tests for config bootstrap (task 5.1)

- 9 Unity tests covering Req 3.1-3.5: immediate return on nonzero tag,
  all-zero peers no defer, peer tag>0 sets defer_config_fetch, probe
  error codes, deferred fetch preconditions, ha_init zero invariant
- Linker fails with undefined refs to bootstrap_config_if_needed
  and xce_probe_config_tag (expected RED proof)

src/controller/meson.build

@@ -103,6 +103,7 @@ controller_unit_test_src = [
   'testsuite/test_worker_join.c',
   'testsuite/test_ha_startup.c',
   'testsuite/test_ha_election.c',
+  'testsuite/test_ha_bootstrap.c',
   'startup_validation.c',
   'worker.c',
   'persist.c',