feat: add component-aware RFC 5424 application logging system

- Modify Rfc5424Formatter to read decnet_component from LogRecord
  and use it as RFC 5424 APP-NAME field (falls back to 'decnet')
- Add get_logger(component) factory in decnet/logging/__init__.py
  with _ComponentFilter that injects decnet_component on each record
- Wire all five layers to their component tag:
    cli -> 'cli', engine -> 'engine', api -> 'api' (api.py, ingester,
    routers), mutator -> 'mutator', collector -> 'collector'
- Add structured INFO/DEBUG/WARNING/ERROR log calls throughout each
  layer per the defined vocabulary; DEBUG calls are suppressed unless
  DECNET_DEVELOPER=true
- Add tests/test_logging.py covering factory, filter, formatter
  component-awareness, fallback behaviour, and level gating

decnet/web/router/stream/api_stream_events.py

@@ -1,15 +1,15 @@
 import json
 import asyncio
-import logging
 from typing import AsyncGenerator, Optional
 
 from fastapi import APIRouter, Depends, Query, Request
 from fastapi.responses import StreamingResponse
 
 from decnet.env import DECNET_DEVELOPER
+from decnet.logging import get_logger
 from decnet.web.dependencies import get_stream_user, repo
 
-log = logging.getLogger(__name__)
+log = get_logger("api")
 
 router = APIRouter()