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_decky.py

@@ -1,6 +1,7 @@
 import os
 from fastapi import APIRouter, Depends, HTTPException, Path
 
+from decnet.telemetry import traced as _traced
 from decnet.mutator import mutate_decky
 from decnet.web.dependencies import require_admin, repo
 
@@ -12,6 +13,7 @@ router = APIRouter()
     tags=["Fleet Management"],
     responses={401: {"description": "Could not validate credentials"}, 403: {"description": "Insufficient permissions"}, 404: {"description": "Decky not found"}}
 )
+@_traced("api.mutate_decky")
 async def api_mutate_decky(
     decky_name: str = Path(..., pattern=r"^[a-z0-9\-]{1,64}$"),
     admin: dict = Depends(require_admin),