Phase 4.7 — Spring Boot starter plugins depend on. Provides: * @PluginCapability and @PluginEndpoint annotations, * RegistrationLifecycleBean (handshake on ApplicationReadyEvent), * HeartbeatPublisher (@Scheduled), * Auto-configuration that builds the registration payload from application.yml, * Default exception handler that maps thrown exceptions to PluginErrorResponse. Plugin authors include this module + write capability beans; the ...