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/reference.py

@@ -0,0 +1,39 @@
+"""Reference and duplicate group models."""
+from sqlalchemy import Float, ForeignKey, JSON, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base, TimestampMixin, UUIDMixin
+
+
+class ArticleReference(Base, UUIDMixin, TimestampMixin):
+    """Reference from a cleaned article to another related article."""
+
+    __tablename__ = "article_references"
+
+    source_article_id: Mapped[str] = mapped_column(
+        ForeignKey("cleaned_articles.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    referenced_article_id: Mapped[str | None] = mapped_column(
+        ForeignKey("cleaned_articles.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    reference_type: Mapped[str] = mapped_column(String(64), nullable=False, index=True)
+    reference_link: Mapped[str | None] = mapped_column(String(2048), default="")
+    reference_title: Mapped[str | None] = mapped_column(String(1024), default="")
+    similarity: Mapped[float | None] = mapped_column(Float, nullable=True)
+
+
+class DuplicateGroup(Base, UUIDMixin, TimestampMixin):
+    """Group of duplicate articles."""
+
+    __tablename__ = "duplicate_groups"
+
+    representative_article_id: Mapped[str | None] = mapped_column(
+        ForeignKey("cleaned_articles.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    member_article_ids: Mapped[list] = mapped_column(JSON, default=list, nullable=False)
+    similarity_matrix: Mapped[dict] = mapped_column(JSON, default=dict, nullable=False)
+    brief_date: Mapped[str | None] = mapped_column(String(10), default="", index=True)
+
+    articles: Mapped[list["CleanedArticle"]] = relationship(
+        "CleanedArticle", back_populates="duplicate_group"
+    )