add WebSocket debug.log streaming for standalone mode

[tequdev]

Summary

• Add a sidecar container (debugstream) that streams debug.log lines via WebSocket, filtered by r-address
• Endpoint: ws://localhost:9999/debugstream/{raddress} — only lines matching the given address are sent
• Uses a Docker named volume ({protocol}-log) shared between xahaud and debugstream containers (no host sync needed)
• Volume is ephemeral — cleaned up on docker compose down -v via stop.sh

Changes

• New: deploykit/debugstream/server.py — aiohttp-based WebSocket server with async tail-follow
• New: deploykit/debugstream/Dockerfile — lightweight Python 3.12-slim container
• Modified: main.py — integrate debugstream into create_xahau_standalone_folder(), switch log volume from bind mount to named volume
• Modified: deploy_kit.py — add build_debugstream_service(), update stop script with -v flag
• Modified: cli.py — add --debugstream_port option (default: 9999)
• New: tests/test_debugstream.py — 8 unit tests

Scope

• Xahau standalone (up:standalone) only. XRPL image mode accepts the parameter but does not use it.

Test plan

• poetry run pytest tests/unit tests/test_debugstream.py — all 55 tests pass
• Run xrpld-netgen up:standalone and verify debugstream container starts
• Connect via wscat -c ws://localhost:9999/debugstream/{raddress} and confirm filtered log lines are streamed