fix(M4): correction des 10 FIXME — client pronotepy, repli unique, couverture 95%

Branch fix/m4-fixme fusionnée depuis feature/m4-sources-pronote.

Corrections:
- Client pronotepy : ENT_RESOLVERS (30 callables), factory
  ParentClient/Client, pronote_url/account_type, propagation erreurs
- fallback.py : repli unique (non réciproque), filtre target_date,
  from None sur PipelineCriticalError, fetch_messages/informations
  log + re-raise
- ical.py : STATUS:CANCELLED sans CATEGORIES, blocs multi-dates
- .env.example : PRONOTE_URL, PRONOTE_ACCOUNT_TYPE
- Tests : 150 tests, couverture 93.34% (sources/pronote/ 95%)
- Docs : TODO.md M4 coché, GUIDE synchronisé

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

# Conflicts:
#	GUIDE_DEV_PYTHON.md
#	TODO.md

.secrets.baseline

@@ -139,11 +139,11 @@
         "type": "Hex High Entropy String",
         "filename": "GUIDE_DEV_PYTHON.md",
         "hashed_secret": "90bd1b48e958257948487b90bee080ba5ed00caa",
-        "is_secret": false,
         "is_verified": true,
-        "line_number": 5117
+        "line_number": 4893,
+        "is_secret": false
       }
     ]
   },
-  "generated_at": "2026-09-05T21:51:55Z"
+  "generated_at": "2026-09-06T14:37:44Z"
 }