Co-Authored-By: Codex <noreply@anthropic.com>

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.