Add Reddit monitoring bot — backend, frontend, and Docker config

Python/FastAPI backend with PostgreSQL for collecting Reddit data via
public .json endpoints. React/Vite dashboard for analytics. Docker Compose
setup with API and worker services connecting to shared PostgreSQL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/models/subreddit.py

@@ -0,0 +1,28 @@
+from datetime import datetime, timezone
+from sqlalchemy import String, Boolean, Integer, DateTime
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from backend.models.base import Base
+
+
+class MonitoredSubreddit(Base):
+    __tablename__ = "monitored_subreddits"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(255), unique=True, nullable=False)
+    display_name: Mapped[str | None] = mapped_column(String(255))
+    description: Mapped[str | None] = mapped_column()
+    subscribers: Mapped[int | None] = mapped_column(Integer)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc),
+    )
+
+    posts: Mapped[list["Post"]] = relationship(back_populates="subreddit")  # noqa: F821
+    daily_digests: Mapped[list["DailyDigest"]] = relationship(back_populates="subreddit")  # noqa: F821
+    summaries: Mapped[list["Summary"]] = relationship(back_populates="subreddit")  # noqa: F821