Add Dify integration and enhance workflow node specifications

- Introduce new fields `dify_api_url` and `dify_api_key` in `AssistantConfig` for Dify API integration.
- Update `requirements.txt` to include `dify-client-python` for Dify SDK support.
- Modify `config_resolver` to handle Dify connection information.
- Add a new `globalNode` type in workflow specifications to provide unified settings across workflows.
- Enhance node specifications with additional constraints and default values for better configuration management.
- Update frontend components to support the new `globalNode` type and its properties, improving workflow editor functionality.

frontend/src/lib/api.ts

@@ -338,6 +338,7 @@ export type NodeFieldSpec = {
   label: string;
   type: "text" | "textarea" | "switch";
   required?: boolean;
+  default?: unknown;
 };
 
 export type NodeConstraints = {
@@ -345,6 +346,8 @@ export type NodeConstraints = {
   maxIncoming?: number;
   minOutgoing?: number;
   maxOutgoing?: number;
+  minInstances?: number;
+  maxInstances?: number;
 };
 
 export type NodeSpecDto = {