Add node simulator test script for TCP push testing

[jonnyspicer]

Summary

Create a standalone Python script that simulates a radar node pushing detection frames over TCP, for use in testing and debugging the TCP push pipeline.

Context

Depends on #6 (TcpServer + TcpReceiver) being complete to test against.

See design spec: docs/superpowers/specs/2026-03-11-tcp-push-detection-forwarding-design.md in the retina monorepo.

Deliverable

tests/simulate_node.py

A CLI tool that connects to tracker-host's TCP server and sends detection frames. Serves as both a test fixture and a manual debugging tool.

Scenarios to support

• Normal stream — send synthetic detection frames at configurable CPI rate (default 0.5s)
• Disconnect/reconnect — close socket after N frames, reconnect after configurable delay
• Multiple nodes — simulate N concurrent nodes with different node_ids
• Invalid token — connect with wrong token, verify rejection
• Malformed JSON — send garbage data, verify server handles gracefully
• Buffer burst — simulate reconnect with a burst of buffered frames (rapid send of N frames)
• Heartbeat only — connect and send only heartbeats, no detections

CLI interface

# Basic: single node, continuous stream
python tests/simulate_node.py --host localhost --port 30050 --node-id radar-test --token secret

# Multiple nodes
python tests/simulate_node.py --host localhost --port 30050 --nodes 3 --token secret

# Disconnect/reconnect scenario
python tests/simulate_node.py --host localhost --port 30050 --node-id radar-test --token secret --disconnect-after 10 --reconnect-delay 5

# Buffer burst on reconnect
python tests/simulate_node.py --host localhost --port 30050 --node-id radar-test --token secret --disconnect-after 10 --reconnect-delay 5 --buffer-burst 50

Detection frame format

Generate realistic synthetic frames with:

• Monotonically increasing timestamps
• 1-5 random detections per frame (random delay/doppler/snr values in plausible ranges)
• Optional synthetic ADS-B matches

Acceptance criteria

• Script connects and sends valid newline-delimited JSON frames
• All scenarios listed above are supported via CLI flags
• Frames include node_id and token
• Heartbeats sent during idle periods
• Clean disconnect handling
• Useful log output showing what's being sent