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>

alembic/versions/270efe6976bc_initial_migration_channel_and_.py

@@ -0,0 +1,54 @@
+"""Initial migration: Channel and VideoEntry tables
+
+Revision ID: 270efe6976bc
+Revises: 
+Create Date: 2025-11-26 13:55:52.270543
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '270efe6976bc'
+down_revision: Union[str, Sequence[str], None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('channels',
+    sa.Column('id', sa.Integer(), nullable=False),
+    sa.Column('channel_id', sa.String(length=50), nullable=False),
+    sa.Column('title', sa.String(length=200), nullable=False),
+    sa.Column('link', sa.String(length=500), nullable=False),
+    sa.Column('last_fetched', sa.DateTime(), nullable=False),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_channels_channel_id'), 'channels', ['channel_id'], unique=True)
+    op.create_table('video_entries',
+    sa.Column('id', sa.Integer(), nullable=False),
+    sa.Column('channel_id', sa.Integer(), nullable=False),
+    sa.Column('title', sa.String(length=500), nullable=False),
+    sa.Column('link', sa.String(length=500), nullable=False),
+    sa.Column('created_at', sa.DateTime(), nullable=False),
+    sa.ForeignKeyConstraint(['channel_id'], ['channels.id'], ),
+    sa.PrimaryKeyConstraint('id'),
+    sa.UniqueConstraint('link')
+    )
+    op.create_index('idx_channel_created', 'video_entries', ['channel_id', 'created_at'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index('idx_channel_created', table_name='video_entries')
+    op.drop_table('video_entries')
+    op.drop_index(op.f('ix_channels_channel_id'), table_name='channels')
+    op.drop_table('channels')
+    # ### end Alembic commands ###