feat(M3): modèles de données Pydantic (22 modèles, 10 modules)

Modèles créés :
- models/agenda.py : Status, LessonStatus, HomeworkBlock, Lesson (frozen),
  SchoolEventKind, SchoolEvent (frozen), TheoreticalLesson (frozen)
- models/homework.py : Homework (frozen)
- models/message.py : MessageType, Message (frozen)
- models/blog.py : BlogArticle (frozen), ExternalInfo (mutable)
- models/diff.py : AgendaChangeType, AgendaChange (frozen), AgendaDiff (frozen)
- models/pronote.py : PronoteData (mutable)
- models/sync.py : CalDAVSyncStatus, CalDAVSyncPlan, CalDAVSyncResult (mutable)
- models/synthesis.py : SynthesisInput, SynthesisResult (mutable)
- models/xmpp.py : XmppMessage (frozen, external_info: ExternalInfo | None)
- models/__init__.py : ré-export des 22 modèles via __all__

Conventions appliquées :
- Pydantic v2 : model_config = ConfigDict(frozen=True), pas de json_encoders
- StrEnum au lieu de (str, Enum) (ruff UP042)
- Alias _date/_time pour éviter collision champ date/type date
- Sphinx/reST docstrings sur toutes les classes
- TODO.md : 11 items M3 cochés

Validations (@verifier) :
- ruff check : PASS (0 error)
- ruff format --check : PASS (10 fichiers)
- mypy strict : PASS (10 fichiers)
- bandit : PASS (0 issue)
- import 22 modèles : OK
- sérialisation JSON (frozen + mutable) : OK
- frozen immuable, PronoteData/CalDAVSyncResult mutable : OK
- StrEnum isinstance str : OK
- pytest : 0 test (infrastructure OK)

Co-authored-by: OpenCode/orchestrator <opencode-orchestrator@agents.invalid>

pronote_sync/models/__init__.py

@@ -0,0 +1,44 @@
+"""Modèles de données Pydantic pour le pipeline pronote-sync."""
+
+from pronote_sync.models.agenda import (
+    HomeworkBlock,
+    Lesson,
+    LessonStatus,
+    SchoolEvent,
+    SchoolEventKind,
+    Status,
+    TheoreticalLesson,
+)
+from pronote_sync.models.blog import BlogArticle, ExternalInfo
+from pronote_sync.models.diff import AgendaChange, AgendaChangeType, AgendaDiff
+from pronote_sync.models.homework import Homework
+from pronote_sync.models.message import Message, MessageType
+from pronote_sync.models.pronote import PronoteData
+from pronote_sync.models.sync import CalDAVSyncPlan, CalDAVSyncResult, CalDAVSyncStatus
+from pronote_sync.models.synthesis import SynthesisInput, SynthesisResult
+from pronote_sync.models.xmpp import XmppMessage
+
+__all__ = [
+    "AgendaChange",
+    "AgendaChangeType",
+    "AgendaDiff",
+    "BlogArticle",
+    "CalDAVSyncPlan",
+    "CalDAVSyncResult",
+    "CalDAVSyncStatus",
+    "ExternalInfo",
+    "Homework",
+    "HomeworkBlock",
+    "Lesson",
+    "LessonStatus",
+    "Message",
+    "MessageType",
+    "PronoteData",
+    "SchoolEvent",
+    "SchoolEventKind",
+    "Status",
+    "SynthesisInput",
+    "SynthesisResult",
+    "TheoreticalLesson",
+    "XmppMessage",
+]