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/file_handler.py

@@ -13,6 +13,8 @@ import logging.handlers
 import os
 from pathlib import Path
 
+from decnet.telemetry import traced as _traced
+
 _LOG_FILE_ENV = "DECNET_LOG_FILE"
 _DEFAULT_LOG_FILE = "/var/log/decnet/decnet.log"
 _MAX_BYTES = 10 * 1024 * 1024  # 10 MB
@@ -22,10 +24,10 @@ _handler: logging.handlers.RotatingFileHandler | None = None
 _logger: logging.Logger | None = None
 
 
-def _get_logger() -> logging.Logger:
+@_traced("logging.init_file_handler")
+def _init_file_handler() -> logging.Logger:
+    """One-time initialisation of the rotating file handler."""
     global _handler, _logger
-    if _logger is not None:
-        return _logger
 
     log_path = Path(os.environ.get(_LOG_FILE_ENV, _DEFAULT_LOG_FILE))
     log_path.parent.mkdir(parents=True, exist_ok=True)
@@ -46,6 +48,12 @@ def _get_logger() -> logging.Logger:
     return _logger
 
 
+def _get_logger() -> logging.Logger:
+    if _logger is not None:
+        return _logger
+    return _init_file_handler()
+
+
 def write_syslog(line: str) -> None:
     """Write a single RFC 5424 syslog line to the rotating log file."""
     try: