refactor: migrate entity IDs from number to UUID

[Netsbump]

• Update all entities (Exercise, ExerciseType, Video, Test) to use UUID as primary key
• Modify services and controllers to handle UUID strings instead of numbers
• Update DTOs and schemas in packages/schemas to reflect UUID type changes
• Adjust e2e tests to use UUID format for ID testing
• Update database configuration to use gen_random_uuid() for PostgreSQL