feat(log): suppress successful MCP access logs in health filter

Extend `_HealthAccessFilter` to also drop uvicorn access log lines for
successful `POST /mcp` requests, in addition to the existing
`/live`, `/ready`, and `/metrics` health probes.

**Why:** Every Daedalus health poll and tool call hits the single `/mcp`
route. Pallas already emits structured `mcp_request_start` /
`mcp_request_complete` logs at the agent layer, making the uvicorn
access line pure duplication and noise in syslog.

**How:**
- Replace the simple substring list `_HEALTH_PATHS` with compiled regex
  patterns (`_HEALTH_PATH_RE`, `_MCP_RE`) for more precise path matching
- Add `_SUCCESS_STATUS_RE` to only suppress 1xx/2xx/3xx responses;
  non-successful responses (4xx, 5xx) still pass through as real signals
- Update docstring to document the new suppression rules clearly

pallas/log.py

@@ -17,6 +17,7 @@ Level conventions (Ouranos Lab — Python services use UPPERCASE):
 
 import json
 import logging
+import re
 from datetime import datetime, timezone
 
 
@@ -37,17 +38,33 @@ class _JSONFormatter(logging.Formatter):
 
 
 class _HealthAccessFilter(logging.Filter):
-    """Drop uvicorn access log lines for health/metrics endpoints.
+    """Drop uvicorn access log lines for routine 2xx/3xx probes.
 
-    Health check success is the *absence* of errors, not the presence of 200s.
-    Logging every HAProxy probe at INFO floods syslog with noise.
+    Health check success is the *absence* of errors, not the presence of 200s
+    (Ouranos Red Panda standard).  Suppresses:
+
+    * Successful probes to ``/live``, ``/ready``, ``/metrics``
+    * Successful ``POST /mcp`` calls — the MCP endpoint is single-route, every
+      Daedalus health poll and tool call lands there.  Pallas already emits
+      its own structured ``mcp_request_start`` / ``mcp_request_complete`` logs
+      at the agent layer, so the uvicorn access line is pure duplication.
+
+    Non-2xx/3xx responses still pass through — a failing probe or a 5xx on
+    ``/mcp`` is a real signal.
     """
 
-    _HEALTH_PATHS = (" GET /live ", " GET /ready ", " GET /metrics ")
+    _HEALTH_PATH_RE = re.compile(r'"GET /(?:live|ready|metrics)(?:/|\?|\s|")')
+    _MCP_RE = re.compile(r'"POST /mcp(?:/|\?|\s|")')
+    _SUCCESS_STATUS_RE = re.compile(r'" (?:1\d\d|2\d\d|3\d\d)(?:\s|$)')
 
     def filter(self, record: logging.LogRecord) -> bool:
         msg = record.getMessage()
-        return not any(path in msg for path in self._HEALTH_PATHS)
+        is_routine = bool(
+            self._HEALTH_PATH_RE.search(msg) or self._MCP_RE.search(msg)
+        )
+        if is_routine and self._SUCCESS_STATUS_RE.search(msg):
+            return False
+        return True
 
 
 def setup_logging() -> None: