test(ha-config-bootstrap): add failing startup validation tests (task 2.1)

RED-phase tests for 4 startup validation functions — all fail at link time
because the functions under test do not exist yet:
- validate_peer_count: even N>1 returns -EINVAL, odd N returns 0
- validate_cert_files: missing cert/key returns -ENOENT with full path
  in err_buf output param (asserted via strstr)
- validate_vcpus: vcpus<=0 returns -EINVAL, positive returns 0
- validate_startup_config: vcpus key in config returns 0 (not fatal)
  and writes deprecation text into warn_buf (asserted via strstr)

src/controller/testsuite/controller_test.c

@@ -34,6 +34,7 @@ extern void test_p3_manual_failover(void);
 extern void test_ctrl_metrics(void);
 extern void test_config_repl(void);
 extern void test_worker_join(void);
+extern void test_ha_startup(void);
 
 void setUp(void) { return; }
 
@@ -137,6 +138,7 @@ int main(int argc, char* argv[])
     TEST(test_ctrl_metrics);
     TEST(test_config_repl);
     TEST(test_worker_join);
+    TEST(test_ha_startup);
 
     return UNITY_END();
 }