💰 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_extra.go

@@ -0,0 +1,24 @@
+package model
+
+// GetModelEnableGroups 返回指定模型名称可用的用户分组列表。
+// 复用缓存的定价映射，避免额外的数据库查询。
+func GetModelEnableGroups(modelName string) []string {
+    for _, p := range GetPricing() {
+        if p.ModelName == modelName {
+            return p.EnableGroup
+        }
+    }
+    return make([]string, 0)
+}
+
+// GetModelQuotaType 返回指定模型的计费类型（quota_type）。
+// 复用缓存的定价映射，避免额外数据库查询。
+// 如果未找到对应模型，默认返回 0。
+func GetModelQuotaType(modelName string) int {
+    for _, p := range GetPricing() {
+        if p.ModelName == modelName {
+            return p.QuotaType
+        }
+    }
+    return 0
+}