- Add ChannelSender interface for sending heartbeat results to users
- Add sendResponse() to automatically deliver results to last channel
- Add createDefaultHeartbeatTemplate() for first-run setup
- Support HEARTBEAT_OK silent response (legacy compatibility)
- Add structured logging with INFO/ERROR levels
- Move integration tests to separate file with build tag
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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