feat(akte): FILE-009 Freitext-Notizen an beliebiger Ressource

Polymorphes akte_notiz-Modell (gleiches entitaet_typ/entitaet_id-Muster wie
Dokument/Historie/Mangel), CRUD-Endpunkte, NotizenPanel im Akte-Grid. Löschen
nur durch Autor oder Administrator.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVgbozhYmuEhiEJHffRXCV

backend/app/api/v1/api.py

@@ -16,6 +16,7 @@ from app.api.v1.endpoints import (
     lager,
     lagerbewegung,
     mangel,
+    notiz,
     objekte,
     permission,
     personal,
@@ -44,6 +45,7 @@ api_router.include_router(personal.router, tags=["personal"])
 api_router.include_router(mangel.router, tags=["mangel"])
 api_router.include_router(lagerbewegung.router, tags=["lagerbewegung"])
 api_router.include_router(dokument.router, tags=["dokument"])
+api_router.include_router(notiz.router, tags=["notiz"])
 api_router.include_router(permission.router, tags=["permission"])
 api_router.include_router(akte.router, tags=["akte"])
 api_router.include_router(lager.router, tags=["lager"])