Wire NatsStatusTracker into actual NATS client callbacks

[mvillmow]

NatsStatusTracker was designed to be updated by a NATS client, but no NATS client exists yet in the codebase. When nats.c integration is implemented, the connection callbacks (connected, disconnected, reconnecting) must call the corresponding NatsStatusTracker methods. This should be a first-class requirement of the nats.c integration story.

Follow-up from #93

[mvillmow]

[myrmidon-swarm classification: HARD — deferred]

This issue has been classified as HARD by the myrmidon swarm triage pass and is deferred from the current implementation run.

Reasons for HARD classification typically include:

• End-to-end NATS/JetStream integration requiring a live NATS server
• TSan-incompatible dependencies (e.g. concurrentqueue + -fsanitize=thread)
• Architectural cross-subsystem wiring (TransparentBridge, MessageBus ↔ NATSListener)
• Multi-phase changes requiring other HARD issues to land first
• Real external service integration tests

This issue will be addressed in a future implementation wave.