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/internal/httpapi/handlers.go

@@ -580,12 +580,20 @@ func (s *Server) listModels(w http.ResponseWriter, r *http.Request) {
 // @Tags playground
 // @Produce json
 // @Security BearerAuth
+// @Param usage_scene query string false "模型可选场景；不传时保持原有行为" Enums(canvas_model_node,desktop)
 // @Success 200 {object} PlatformModelListResponse
+// @Failure 400 {object} ErrorEnvelope
 // @Failure 401 {object} ErrorEnvelope
+// @Failure 502 {object} ErrorEnvelope
 // @Failure 500 {object} ErrorEnvelope
 // @Router /api/v1/models [get]
 // @Router /api/v1/playground/models [get]
 func (s *Server) listPlayableModels(w http.ResponseWriter, r *http.Request) {
+	usageScene, err := parseModelUsageSceneQuery(r.URL.Query())
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	user, _ := auth.UserFromContext(r.Context())
 	models, err := s.store.ListAccessiblePlatformModels(r.Context(), user)
 	if err != nil {
@@ -593,6 +601,15 @@ func (s *Server) listPlayableModels(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, "list playable models failed")
 		return
 	}
+	if usageScene != "" {
+		availableModelIDs, sceneErr := s.listServerMainUsageSceneModelIDs(r.Context(), usageScene)
+		if sceneErr != nil {
+			s.logger.Error("filter playable models by usage scene failed", "usage_scene", usageScene, "error", sceneErr)
+			writeError(w, http.StatusBadGateway, "model usage scene catalog is unavailable")
+			return
+		}
+		models = filterPlatformModelsByUsageSceneIDs(models, availableModelIDs)
+	}
 	writeJSON(w, http.StatusOK, map[string]any{"items": s.platformModelResponses(r.Context(), models)})
 }