Initial commit: RSS platform phase 1 skeleton with code review fixes

Features:
- FastAPI + SQLAlchemy 2.0 async + PostgreSQL/pgvector + Redis backend
- Vue 3 + TypeScript + Element Plus frontend
- JWT auth with access/refresh tokens and revocation
- Admin/member RBAC
- RSS feed CRUD and article listing
- Settings management with Fernet encryption for sensitive values
- Redis distributed lock service
- Alembic initial migration
- Docker Compose development environment

Fixes from code review:
- Fix DB session leak in dependency injection
- Restrict registration to admin only
- Add default admin password warning
- Implement JWT refresh tokens and jti blacklist
- Strengthen password policy
- Use func.count for pagination totals
- Replace NullPool with AsyncAdaptedQueuePool
- Remove init_db from lifespan to enforce alembic migrations
- Add request_id middleware and logging filter
- Fix vite.config.ts env loading
- Add frontend token refresh interceptor
- Add Vue error handler

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/models/base.py

@@ -0,0 +1,45 @@
+"""SQLAlchemy 2.0 async base and session factory."""
+from datetime import datetime, timezone
+from uuid import uuid4
+
+from sqlalchemy import DateTime, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+
+
+class Base(DeclarativeBase):
+    """Base class for all models."""
+
+    pass
+
+
+class TimestampMixin:
+    """Adds created_at and updated_at columns."""
+
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        nullable=False,
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+        nullable=False,
+    )
+
+
+class UUIDMixin:
+    """Adds UUID primary key."""
+
+    id: Mapped[str] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+        index=True,
+    )
+
+
+def utc_now() -> datetime:
+    """Return timezone-aware UTC now."""
+    return datetime.now(timezone.utc)