test(ws): WebSocket subscription tests (#105)

[Nuel-ship-it]

Summary

Closes #105

Adds tests/integration/ws.test.ts — a self-contained Jest test suite for the /subscribe/:address WebSocket endpoint. No Docker or database required; the suite spins up a real http.createServer + attachWebSocketServer in-process.

Tests

Test	Covers
Rejects upgrade on unknown path	404 / socket destroy path
Connects and receives a matching transfer	connect / sub / recv cycle
Receives outgoing transfers (sender match)	fromAddress filter branch
Does not forward transfers for a different address	address isolation
Connect / subscribe / receive / disconnect cycle — cleans up listener	clean disconnect, no dangling emitter
Backpressure — 50 rapid messages without error	fast-producer / slow-consumer buffering

Acceptance criteria

• Connect/sub/recv/disc cycle works
• Backpressure on slow client tested

Verified

PASS  tests/integration/ws.test.ts (7.302 s)
  WebSocket /subscribe/:address
    ✓ rejects upgrade on unknown path with 404
    ✓ connects and receives a matching transfer
    ✓ receives outgoing transfers (sender match)
    ✓ does not forward transfers for a different address
    ✓ connect / subscribe / receive / disconnect cycle — cleans up listener
    ✓ backpressure — buffers many rapid messages without error

Tests: 6 passed, 6 total

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