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/web/router/fleet/api_mutate_interval.py

@@ -1,5 +1,6 @@
 from fastapi import APIRouter, Depends, HTTPException
 
+from decnet.telemetry import traced as _traced
 from decnet.config import DecnetConfig
 from decnet.web.dependencies import require_admin, repo
 from decnet.web.db.models import MutateIntervalRequest
@@ -24,6 +25,7 @@ def _parse_duration(s: str) -> int:
         422: {"description": "Validation error"}
     },
 )
+@_traced("api.update_mutate_interval")
 async def api_update_mutate_interval(decky_name: str, req: MutateIntervalRequest, admin: dict = Depends(require_admin)) -> dict[str, str]:
     state_dict = await repo.get_state("deployment")
     if not state_dict: