- Add flowchart_version_history table to store snapshots after generate/refine
- Create versions API endpoint (GET list, POST restore)
- Add History tab with version list showing source, validation status, timestamp
- Implement inline preview mode to view historical versions without restoring
- Preview mode shows amber banner and updates diagram, examples, worksheet, tests
- Hide structure/input tabs (not useful currently)
- Add preview notice in refinement panel clarifying behavior
- Update React Query documentation with comprehensive patterns
- Add versionHistoryKeys to central query key factory
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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