Add TCP push client for detection forwarding

[jonnyspicer]

Summary

• Adds TCP push client to api/server.js that forwards detection frames to a remote tracker-host over persistent TCP connections
• Uses newline-delimited JSON framing with node_id and token in every frame
• Ring buffer (configurable buffer_max, default 1000) stores frames during disconnects, drains on reconnect
• Heartbeat keepalives every 10 seconds during idle periods
• TCP_NODELAY for low-latency forwarding
• Automatic reconnection with backoff on connection loss
• New config fields: network.tracker_forward.token, buffer_max, heartbeat_interval_sec

Test plan

• Tested locally with tracker-host TCP server and node simulator
• Deploy to a single test node first (Phase 2 of rollout)
• Run in dual-mode alongside HTTP polling to compare data streams
• Monitor reconnect behavior, buffer drain, heartbeat keepalives

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