feat(models): 支持按使用场景筛选模型

Gateway 模型接口校验 usage_scene，并与 server-main 严格场景目录取交集；显式场景查询在上游不可用时关闭失败，避免返回不应暴露的模型。\n\n验证：env -u AI_GATEWAY_TEST_DATABASE_URL go test ./... -count=1

apps/api/docs/swagger.yaml

@@ -8381,6 +8381,14 @@ paths:
   /api/v1/models:
     get:
       description: 按当前用户权限返回可用于 Playground 或 API 调用的模型列表。
+      parameters:
+      - description: 模型可选场景；不传时保持原有行为
+        enum:
+        - canvas_model_node
+        - desktop
+        in: query
+        name: usage_scene
+        type: string
       produces:
       - application/json
       responses:
@@ -8388,6 +8396,10 @@ paths:
           description: OK
           schema:
             $ref: '#/definitions/httpapi.PlatformModelListResponse'
+        "400":
+          description: Bad Request
+          schema:
+            $ref: '#/definitions/httpapi.ErrorEnvelope'
         "401":
           description: Unauthorized
           schema:
@@ -8396,6 +8408,10 @@ paths:
           description: Internal Server Error
           schema:
             $ref: '#/definitions/httpapi.ErrorEnvelope'
+        "502":
+          description: Bad Gateway
+          schema:
+            $ref: '#/definitions/httpapi.ErrorEnvelope'
       security:
       - BearerAuth: []
       summary: 列出可调用模型
@@ -8615,6 +8631,14 @@ paths:
   /api/v1/playground/models:
     get:
       description: 按当前用户权限返回可用于 Playground 或 API 调用的模型列表。
+      parameters:
+      - description: 模型可选场景；不传时保持原有行为
+        enum:
+        - canvas_model_node
+        - desktop
+        in: query
+        name: usage_scene
+        type: string
       produces:
       - application/json
       responses:
@@ -8622,6 +8646,10 @@ paths:
           description: OK
           schema:
             $ref: '#/definitions/httpapi.PlatformModelListResponse'
+        "400":
+          description: Bad Request
+          schema:
+            $ref: '#/definitions/httpapi.ErrorEnvelope'
         "401":
           description: Unauthorized
           schema:
@@ -8630,6 +8658,10 @@ paths:
           description: Internal Server Error
           schema:
             $ref: '#/definitions/httpapi.ErrorEnvelope'
+        "502":
+          description: Bad Gateway
+          schema:
+            $ref: '#/definitions/httpapi.ErrorEnvelope'
       security:
       - BearerAuth: []
       summary: 列出可调用模型