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/logging/forwarder.py

@@ -11,6 +11,8 @@ shared utilities for validating and parsing the log_target string.
 
 import socket
 
+from decnet.telemetry import traced as _traced
+
 
 def parse_log_target(log_target: str) -> tuple[str, int]:
     """
@@ -23,6 +25,7 @@ def parse_log_target(log_target: str) -> tuple[str, int]:
     return parts[0], int(parts[1])
 
 
+@_traced("logging.probe_log_target")
 def probe_log_target(log_target: str, timeout: float = 2.0) -> bool:
     """
     Return True if the log target is reachable (TCP connect succeeds).