💰 feat: Add model billing type (quota_type) support across backend & frontend

Summary
• Backend
  1. model/model_meta.go
     – Added `QuotaType` field to `Model` struct (JSON only, gorm `-`).
  2. model/model_groups.go
     – Implemented `GetModelQuotaType(modelName)` leveraging cached pricing map.
  3. controller/model_meta.go
     – Enhanced `fillModelExtra` to populate `QuotaType` using new helper.

• Frontend
  1. web/src/components/table/models/ModelsColumnDefs.js
     – Introduced `renderQuotaType` helper that visualises billing mode with coloured tags (`teal = per-call`, `violet = per-token`).
     – Added “计费类型” column (`quota_type`) to models table.

Why
Providing the billing mode alongside existing pricing/group information gives administrators instant visibility into whether each model is priced per call or per token, aligning UI with new backend metadata.

Notes
No database migration required – `quota_type` is transient, delivered via API. Frontend labels/colours can be adjusted via i18n or theme tokens if necessary.

controller/model_meta.go

@@ -147,5 +147,7 @@ func fillModelExtra(m *model.Model) {
     }
     // 填充启用分组
     m.EnableGroups = model.GetModelEnableGroups(m.ModelName)
+    // 填充计费类型
+    m.QuotaType = model.GetModelQuotaType(m.ModelName)
 
 }