feat: complete OTEL tracing across all services with pipeline bridge and docs

Extends tracing to every remaining module: all 23 API route handlers,
correlation engine, sniffer (fingerprint/p0f/syslog), prober (jarm/hassh/tcpfp),
profiler behavioral analysis, logging subsystem, engine, and mutator.

Bridges the ingester→SSE trace gap by persisting trace_id/span_id columns on
the logs table and creating OTEL span links in the SSE endpoint. Adds log-trace
correlation via _TraceContextFilter injecting otel_trace_id into Python LogRecords.

Includes development/docs/TRACING.md with full span reference (76 spans),
pipeline propagation architecture, quick start guide, and troubleshooting.

decnet/mutator/engine.py

@@ -133,6 +133,7 @@ async def mutate_all(repo: BaseRepository, force: bool = False) -> None:
         log.info("mutate_all: complete mutated_count=%d", mutated_count)
 
 
+@_traced("mutator.watch_loop")
 async def run_watch_loop(repo: BaseRepository, poll_interval_secs: int = 10) -> None:
     """Run an infinite loop checking for deckies that need mutation."""
     log.info("mutator watch loop started poll_interval_secs=%d", poll_interval_secs)