#21 CRITICAL: Schema integrity violations - version types mismatch, nullable definition_id

Multiple schema integrity violations: 1. workflow_run.workflow_version is VARCHAR(50) but workflow_definition.version is INTEGER - can't compare/upgrade 2. workflow_run.definition_id is NULLABLE - allows orphan runs (e.g. 58e6b3b8-e0e9-4a9c-9066-c3b3098ada65) 3. workflow_schedules.definition_id is NULLABLE - schedules without definitions 4. durable_cron.py creates workflows incorrectly without proper definitions FIX: Migration to convert workflow_run.workflow_version to INTEGER, NOT NULL constraints, fix durable_cron.py