Add unit tests for group ratio, cross-group retry, and price calculation:
- Group ratio CRUD and special ratio override (12 tests)
- HandleGroupRatio with auto-group and special ratios (5 tests)
- ModelPriceHelper with group ratio in price/ratio modes (3 tests)
- Channel selection priority, groups, weighted LB (6 tests)
- RetryParam and AutoGroup service logic (7 tests)
Also restore the group pricing card in model detail SideSheet.
Delete leftover channel pricing controllers and routes after removing channel pricing, and align relay price helpers with global pricing plus user channel ratio only.
Co-Authored-By: Codex <noreply@anthropic.com>