feat: Projektfundament mit Datenmodell, Migrationen und Seed

- Repo-Struktur für Backend, Frontend, Dokumentation und Gitea-Workflows
- FastAPI-Skeleton mit pydantic-settings und RFC-7807-artigem Fehlerformat
- Vollständiges Datenmodell (15 Tabellen) als SQLAlchemy-2.0-Modelle
- Alembic gegen die Async-Engine inklusive Erstmigration
- Idempotenter Seed für den deutschen Kategoriebaum und Standardregeln
- Endpunkte /api/health und /api/version
- pytest-Infrastruktur mit transaktionsisolierten Fixtures

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014e7t8UpmoVNMtWivY5LiSH

backend/app/models/__init__.py

@@ -0,0 +1,54 @@
+"""SQLAlchemy-Modelle. Import hier hält Alembics Autogenerate vollständig."""
+
+from app.db.base import Base
+from app.models.core import Account, AppUser, Category, LogoAsset, Merchant
+from app.models.enums import (
+    AccountType,
+    BusinessDayShift,
+    EntryKind,
+    LogoSource,
+    LogoStatus,
+    NotificationChannel,
+    NotificationStatus,
+    NotificationType,
+    OccurrenceStatus,
+)
+from app.models.finance import (
+    AmountVersion,
+    Budget,
+    BudgetTemplate,
+    Occurrence,
+    Recurrence,
+    ReserveLedger,
+    SavingsGoal,
+    Transaction,
+)
+from app.models.notification import NotificationLog, NotificationRule
+
+__all__ = [
+    "Account",
+    "AccountType",
+    "AmountVersion",
+    "AppUser",
+    "Base",
+    "Budget",
+    "BudgetTemplate",
+    "BusinessDayShift",
+    "Category",
+    "EntryKind",
+    "LogoAsset",
+    "LogoSource",
+    "LogoStatus",
+    "Merchant",
+    "NotificationChannel",
+    "NotificationLog",
+    "NotificationRule",
+    "NotificationStatus",
+    "NotificationType",
+    "Occurrence",
+    "OccurrenceStatus",
+    "Recurrence",
+    "ReserveLedger",
+    "SavingsGoal",
+    "Transaction",
+]