Add agent workflow engine foundation and theme-style page switcher.

Introduce WorkflowEngine with state machine, tool registry, and builtin chat template; migrate stream chat to engine callbacks. Move page mode switching to TopBar actions cluster as a ThemeToggle-style dropdown (聊天/工作室/爽文/房间).

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/core/config.py

@@ -61,6 +61,10 @@ class Settings:
 	# 图片资源目录
 	IMAGES_PATH = DATA_PATH / "images"
 
+	# Agent 工作流模板与运行记录
+	AGENT_TEMPLATES_PATH = DATA_PATH / "agent" / "templates"
+	AGENT_RUNS_PATH = DATA_PATH / "agent" / "runs"
+
 	def ensure_directories(self):
 		"""确保所有配置的目录存在，如果不存在则创建"""
 		directories = [
@@ -72,6 +76,8 @@ class Settings:
 			self.COMFYUI_WORKFLOWS_PATH,
 			self.CHARACTERS_PATH,
 			self.IMAGES_PATH,
+			self.AGENT_TEMPLATES_PATH,
+			self.AGENT_RUNS_PATH,
 		]
 		for directory in directories:
 			directory.mkdir(parents=True, exist_ok=True)