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>

.gitignore

@@ -8,3 +8,9 @@ wheels/
 
 # Virtual environments
 .venv
+
+# Database files
+*.db
+*.db-journal
+*.db-shm
+*.db-wal