Fixed two critical issues preventing agent communication:
1. Fix Mix.env() runtime error in production
- Replace Mix.env() with Application.get_env(:towerops, :env)
- Add :env config to test.exs
- Mix module not available in production releases
2. Add Protocol Buffers support to agent API endpoints
- GET /api/v1/agent/config now accepts application/x-protobuf
- POST /api/v1/agent/heartbeat now accepts application/x-protobuf
- Added conversion functions for config/equipment/sensors/interfaces
- Maintains JSON backward compatibility as fallback
All agent controller tests passing (14 tests, 0 failures)
Graham McIntire
9a6369bd27