Restructure: Move 43 files into 8 domain packages (backend-lehrer)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-lehrer/messenger/api.py

@@ -0,0 +1,21 @@
+"""
+BreakPilot Messenger API — Barrel Re-export.
+
+Stellt Endpoints fuer Kontakte, Konversationen, Nachrichten,
+CSV-Import, Gruppenmanagement und Templates bereit.
+
+Split into:
+  - messenger_models.py: Pydantic models
+  - messenger_helpers.py: JSON file storage & default templates
+  - messenger_contacts.py: Contact CRUD & CSV import/export
+  - messenger_conversations.py: Conversations, messages, groups, templates, stats
+"""
+
+from fastapi import APIRouter
+
+from .contacts import router as _contacts_router
+from .conversations import router as _conversations_router
+
+router = APIRouter(prefix="/api/messenger", tags=["Messenger"])
+router.include_router(_contacts_router)
+router.include_router(_conversations_router)