* feat(dashboard): add traffic flow sankey chart
Add dashboard flow APIs and a Sankey-based flow view with user, optional API key, model, and channel layers.\n\nReuse the dashboard VChart palette, add precise link/node tooltips and interactions, and cover filtering, layer ordering, color stability, and error states with tests.
* feat: build flow chart from quota data
---------
Co-authored-by: CaIon <i@caion.me>
- Updated UpdateWithStatus method to use Model().Select("*").Updates() for conditional updates, preventing GORM's INSERT fallback.
- Introduced comprehensive integration tests for UpdateWithStatus, covering scenarios for winning and losing CAS updates, as well as concurrent updates.
- Added task_cas_test.go to validate the new behavior and ensure data integrity during concurrent state transitions.
CaIon