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.

backend/services/brains/registry.py

@@ -1,25 +1,40 @@
-"""类型 → Brain 工厂。新增一种大脑 = 加一个 brain 文件 + 在此注册一行。"""
+"""Explicit assistant-type registry. Unsupported types never silently degrade."""
 
 from __future__ import annotations
 
+from collections.abc import Callable
+
 from models import AssistantConfig
 
 from services.brains.base import Brain, BrainSpec
+from services.brains.dify_brain import DifyBrain
 from services.brains.fastgpt_brain import FastGPTBrain
-from services.brains.internal_brain import InternalBrain
+from services.brains.prompt_brain import PromptBrain
+from services.brains.workflow_brain import WorkflowBrain
+
+
+def _workflow(cfg: AssistantConfig) -> Brain:
+    return WorkflowBrain(cfg.graph)
+
+
+BRAIN_FACTORIES: dict[str, Callable[[AssistantConfig], Brain]] = {
+    "prompt": lambda _cfg: PromptBrain(),
+    "workflow": _workflow,
+    "dify": lambda _cfg: DifyBrain(),
+    "fastgpt": lambda _cfg: FastGPTBrain(),
+}
 
-# 各类型的元数据(供 schema 校验 / realtime 门控复用,无需实例化 Brain)。
 SPECS: dict[str, BrainSpec] = {
-    "prompt": InternalBrain("prompt").spec,
-    "workflow": InternalBrain("workflow").spec,
-    "fastgpt": FastGPTBrain().spec,
+    "prompt": PromptBrain.spec,
+    "workflow": WorkflowBrain.spec,
+    "dify": DifyBrain.spec,
+    "fastgpt": FastGPTBrain.spec,
 }
 
 
 def build_brain(cfg: AssistantConfig) -> Brain:
-    """按 cfg.type 构造每通电话的 Brain 实例(未知类型回退 prompt)。"""
-    if cfg.type == "fastgpt":
-        return FastGPTBrain()
-    if cfg.type in ("prompt", "workflow"):
-        return InternalBrain(cfg.type)
-    return InternalBrain("prompt")
+    try:
+        factory = BRAIN_FACTORIES[cfg.type]
+    except KeyError as exc:
+        raise ValueError(f"尚未实现的助手类型: {cfg.type}") from exc
+    return factory(cfg)