Add SQLAlchemy ORM with Alembic migrations

- Added SQLAlchemy 2.0 and Alembic 1.13 dependencies
- Created models.py with Channel and VideoEntry ORM models
- Created database.py for database configuration and session management
- Initialized Alembic migration system with initial migration
- Updated feed_parser.py with save_to_db() method for persistence
- Updated main.py with database initialization and new API routes:
  - /api/feed now saves to database by default
  - /api/channels lists all tracked channels
  - /api/history/<channel_id> returns video history
- Updated .gitignore to exclude database files
- Updated CLAUDE.md with comprehensive ORM and migration documentation

Database uses SQLite (yottob.db) with upsert logic to avoid duplicates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

models.py

@@ -0,0 +1,62 @@
+"""Database models for YouTube feed storage."""
+
+from datetime import datetime
+from typing import List
+
+from sqlalchemy import String, DateTime, ForeignKey, Index
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship
+
+
+class Base(DeclarativeBase):
+    """Base class for all database models."""
+    pass
+
+
+class Channel(Base):
+    """YouTube channel model."""
+
+    __tablename__ = "channels"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    channel_id: Mapped[str] = mapped_column(String(50), unique=True, nullable=False, index=True)
+    title: Mapped[str] = mapped_column(String(200), nullable=False)
+    link: Mapped[str] = mapped_column(String(500), nullable=False)
+    last_fetched: Mapped[datetime] = mapped_column(DateTime, nullable=False, default=datetime.utcnow)
+
+    # Relationship to video entries
+    videos: Mapped[List["VideoEntry"]] = relationship("VideoEntry", back_populates="channel", cascade="all, delete-orphan")
+
+    def __repr__(self) -> str:
+        return f"<Channel(id={self.id}, channel_id='{self.channel_id}', title='{self.title}')>"
+
+
+class VideoEntry(Base):
+    """YouTube video entry model."""
+
+    __tablename__ = "video_entries"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    channel_id: Mapped[int] = mapped_column(ForeignKey("channels.id"), nullable=False)
+    title: Mapped[str] = mapped_column(String(500), nullable=False)
+    link: Mapped[str] = mapped_column(String(500), unique=True, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, nullable=False, default=datetime.utcnow)
+
+    # Relationship to channel
+    channel: Mapped["Channel"] = relationship("Channel", back_populates="videos")
+
+    # Index for faster queries
+    __table_args__ = (
+        Index('idx_channel_created', 'channel_id', 'created_at'),
+    )
+
+    def __repr__(self) -> str:
+        return f"<VideoEntry(id={self.id}, title='{self.title}', link='{self.link}')>"
+
+    def to_dict(self) -> dict:
+        """Convert to dictionary for API responses."""
+        return {
+            "id": self.id,
+            "title": self.title,
+            "link": self.link,
+            "created_at": self.created_at.isoformat()
+        }