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/daily_digest.py

@@ -0,0 +1,22 @@
+from datetime import date, datetime, timezone
+from sqlalchemy import Date, DateTime, ForeignKey, JSON
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from backend.models.base import Base
+
+
+class DailyDigest(Base):
+    __tablename__ = "daily_digests"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    subreddit_id: Mapped[int] = mapped_column(
+        ForeignKey("monitored_subreddits.id"), nullable=False
+    )
+    digest_date: Mapped[date] = mapped_column(Date, nullable=False)
+    content: Mapped[str] = mapped_column(nullable=False)
+    metadata_: Mapped[dict | None] = mapped_column("metadata", JSON)
+    generated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+
+    subreddit: Mapped["MonitoredSubreddit"] = relationship(back_populates="daily_digests")  # noqa: F821