docs(M11): align GUIDE sections 4.2.1 and 11.3 with FIXME_M11 corrections

GUIDE_DEV_PYTHON.md:
- §11.3: add except PipelineCriticalError: raise before each non-critical
  except in the illustrative PipelineRunner.run() code
- §11.3: replace redact_exception(exc) with self._redact(exc) in all except
  blocks, add explanatory paragraph about _redaction_secrets and _redact()
- §11.3: fix Google-style Returns: to Sphinx/reST :return: and :rtype:
- §11.3: fix malformed Markdown code fence (get_errors/get_warnings orphaned)
- §4.2.1: fix redact_exception() example to pass extra_secrets to
  redact_secrets() in the return statement

TODO.md M11:
- Add and check criterion: PipelineCriticalError from non-blocking step
  stops the pipeline

.secrets.baseline:
- Line numbers updated for documentation shifts

Co-authored-by: opencode/tech-writer <tech-writer@agents.invalid>

.secrets.baseline

@@ -140,7 +140,7 @@
         "filename": "GUIDE_DEV_PYTHON.md",
         "hashed_secret": "90bd1b48e958257948487b90bee080ba5ed00caa",
         "is_verified": true,
-        "line_number": 5029,
+        "line_number": 5064,
         "is_secret": false
       }
     ],
@@ -177,5 +177,5 @@
       }
     ]
   },
-  "generated_at": "2026-09-08T00:29:02Z"
+  "generated_at": "2026-09-08T10:45:46Z"
 }