feat: add OpenTelemetry distributed tracing across all DECNET services

Gated by DECNET_DEVELOPER_TRACING env var (default off, zero overhead).
When enabled, traces flow through FastAPI routes, background workers
(collector, ingester, profiler, sniffer, prober), engine/mutator
operations, and all DB calls via TracedRepository proxy.

Includes Jaeger docker-compose for local dev and 18 unit tests.

decnet/web/ingester.py

@@ -5,6 +5,7 @@ from typing import Any
 from pathlib import Path
 
 from decnet.logging import get_logger
+from decnet.telemetry import traced as _traced
 from decnet.web.db.repository import BaseRepository
 
 logger = get_logger("api")
@@ -83,6 +84,7 @@ async def log_ingestion_worker(repo: BaseRepository) -> None:
         await asyncio.sleep(1)
 
 
+@_traced("ingester.extract_bounty")
 async def _extract_bounty(repo: BaseRepository, log_data: dict[str, Any]) -> None:
     """Detect and extract valuable artifacts (bounties) from log entries."""
     _fields = log_data.get("fields")