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>

database.py

@@ -0,0 +1,71 @@
+"""Database configuration and session management."""
+
+from contextlib import contextmanager
+from typing import Generator
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker, Session
+
+from models import Base
+
+
+# Database configuration
+DATABASE_URL = "sqlite:///yottob.db"
+
+# Create engine
+engine = create_engine(
+    DATABASE_URL,
+    echo=False,  # Set to True for SQL query logging
+    connect_args={"check_same_thread": False}  # Needed for SQLite
+)
+
+# Session factory
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+def init_db() -> None:
+    """Initialize the database by creating all tables.
+
+    This function should be called when the application starts.
+    It creates all tables defined in the models if they don't exist.
+    """
+    Base.metadata.create_all(bind=engine)
+
+
+@contextmanager
+def get_db_session() -> Generator[Session, None, None]:
+    """Context manager for database sessions.
+
+    Usage:
+        with get_db_session() as session:
+            # Use session here
+            session.query(...)
+
+    The session is automatically committed on success and rolled back on error.
+    """
+    session = SessionLocal()
+    try:
+        yield session
+        session.commit()
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()
+
+
+def get_db() -> Generator[Session, None, None]:
+    """Dependency function for Flask routes to get a database session.
+
+    Usage in Flask:
+        session = next(get_db())
+        try:
+            # Use session
+        finally:
+            session.close()
+    """
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()