phsl / new-api

Summary
• Backend
  – Moved duplicate-name validation and total vendor-count aggregation from controllers (`controller/model_meta.go`, `controller/vendor_meta.go`, `controller/prefill_group.go`) to model layer (`model/model_meta.go`, `model/vendor_meta.go`, `model/prefill_group.go`).
  – Added `GetVendorModelCounts()` and `Is*NameDuplicated()` helpers; controllers now call these instead of duplicating queries.
  – API response for `/api/models` now returns `vendor_counts` with per-vendor totals across all pages, plus `all` summary.
  – Removed redundant checks and unused imports, eliminating `go vet` warnings.

• Frontend
  – `useModelsData.js` updated to consume backend-supplied `vendor_counts`, calculate the `all` total once, and drop legacy client-side counting logic.
  – Simplified initial data flow: first render now triggers only one models request.
  – Deleted obsolete `updateVendorCounts` helper and related comments.
  – Ensured search flow also sets `vendorCounts`, keeping tab badges accurate.

Why
This refactor enforces single-responsibility (aggregation in model layer), delivers consistent totals irrespective of pagination, and removes redundant client queries, leading to cleaner code and better performance.