💰 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.

model/model_meta.go

@@ -39,6 +39,7 @@ type Model struct {
 
     BoundChannels []BoundChannel `json:"bound_channels,omitempty" gorm:"-"`
     EnableGroups []string       `json:"enable_groups,omitempty" gorm:"-"`
+    QuotaType    int            `json:"quota_type" gorm:"-"`
 }
 
 // Insert 创建新的模型元数据记录