fix(enrollment): filter Docker bridge IPs and add report_interface/report_ip config

- identity.rs: filter 172.16.0.0/12 (Docker bridge) and 169.254.0.0/16 (link-local)
  from get_ip_addresses() auto-detection
- identity.rs: add is_container_bridge(), is_link_local(),
  get_ip_for_interface(), get_primary_ip() functions
- client.rs: add report_interface/report_ip fields to EnrollmentClient,
  new with_ip_overrides() constructor, register() uses get_primary_ip()
- loader.rs: add report_interface/report_ip to EnrollmentConfig
- mod.rs: wire config overrides through to EnrollmentClient
- config.yaml.example: document new report_interface/report_ip options
- Tests: add 18 new bridge filtering/IP override tests, fix Docker
  container compatibility in existing tests

tests/integration/enrollment_test.rs

@@ -33,8 +33,14 @@ async fn create_mock_manager() -> (MockServer, String) {
 }
 
 /// Build an EnrollmentClient pointing at the mock server.
+/// Uses a test report_ip so enrollment works inside Docker containers
+/// where the only IPs are in the 172.16.0.0/12 bridge range (filtered).
 fn build_client(base_url: &str) -> EnrollmentClient {
-    EnrollmentClient::new(base_url)
+    EnrollmentClient::with_ip_overrides(
+        base_url,
+        None,
+        Some("192.168.1.10".to_string()),
+    )
 }
 
 // =============================================================================