feat(model-test): add image-aware request helpers

frontend/src/api/endpoints/types/model.ts

@@ -59,6 +59,7 @@ export interface Model {
   global_model_display_name?: string
   // 有效配置（合并 Model 和 GlobalModel 的 config）
   effective_config?: Record<string, unknown> | null
+  model_test_capabilities?: ModelTestCapabilities | null
 }
 
 export interface ModelCreate {
@@ -102,6 +103,17 @@ export interface ModelCapabilities {
   [key: string]: boolean
 }
 
+export interface OpenAiImageModelTestCapability {
+  max_generation_count?: number | null
+  supports_generation?: boolean | null
+  supports_edit?: boolean | null
+}
+
+export interface ModelTestCapabilities {
+  'openai:image'?: OpenAiImageModelTestCapability | null
+  [apiFormat: string]: OpenAiImageModelTestCapability | Record<string, unknown> | null | undefined
+}
+
 export interface ProviderModelPriceInfo {
   input_price_per_1m?: number | null
   output_price_per_1m?: number | null
@@ -248,6 +260,7 @@ export interface UpstreamModel {
   owned_by?: string
   display_name?: string
   api_formats: string[]  // 该模型支持的所有 API 格式（后端保证返回数组）
+  model_test_capabilities?: ModelTestCapabilities | null
 }
 
 /**