Initial public release

Aurum — a self-hosted personal finance operating system: cash flow,
net worth tracking, budgets, goals, recurring payments, reports,
proactive alerts, and a compound-interest returns calculator, all
bilingual (RU/EN) and mobile-first. Ships as a three-container Docker
Compose stack (Postgres + FastAPI + nginx-served React frontend).

See README.md for setup and CONTRIBUTING.md for development.

backend/app/models/mixins.py

@@ -0,0 +1,14 @@
+"""Reusable model mixins."""
+from datetime import datetime
+
+from sqlalchemy import DateTime, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+
+class TimestampMixin:
+    """Adds created_at / updated_at columns managed by the database itself."""
+
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )