refactor(config): eliminate global mutable state, wire DeerFlowContext into runtime

- Freeze all config models (AppConfig + 15 sub-configs) with frozen=True
- Purify from_file() — remove 9 load_*_from_dict() side-effect calls
- Replace mtime/reload/push/pop machinery with single ContextVar + init_app_config()
- Delete 10 sub-module globals and their getters/setters/loaders
- Migrate 50+ consumers from get_*_config() to get_app_config().xxx

- Expand DeerFlowContext: app_config + thread_id + agent_name (frozen dataclass)
- Wire into Gateway runtime (worker.py) and DeerFlowClient via context= parameter
- Remove sandbox_id from runtime.context — flows through ThreadState.sandbox only
- Middleware/tools access runtime.context directly via Runtime[DeerFlowContext] generic
- resolve_context() retained at server entry points for LangGraph Server fallback

backend/packages/harness/deerflow/tools/tools.py

@@ -2,7 +2,7 @@ import logging
 
 from langchain.tools import BaseTool
 
-from deerflow.config import get_app_config
+from deerflow.config.app_config import AppConfig
 from deerflow.reflection import resolve_variable
 from deerflow.sandbox.security import is_host_bash_allowed
 from deerflow.tools.builtins import ask_clarification_tool, present_file_tool, task_tool, view_image_tool
@@ -52,7 +52,7 @@ def get_available_tools(
     Returns:
         List of available tools.
     """
-    config = get_app_config()
+    config = AppConfig.current()
     tool_configs = [tool for tool in config.tools if groups is None or tool.group in groups]
 
     # Do not expose host bash by default when LocalSandboxProvider is active.
@@ -123,10 +123,9 @@ def get_available_tools(
     # Add invoke_acp_agent tool if any ACP agents are configured
     acp_tools: list[BaseTool] = []
     try:
-        from deerflow.config.acp_config import get_acp_agents
         from deerflow.tools.builtins.invoke_acp_agent_tool import build_invoke_acp_agent_tool
 
-        acp_agents = get_acp_agents()
+        acp_agents = AppConfig.current().acp_agents
         if acp_agents:
             acp_tools.append(build_invoke_acp_agent_tool(acp_agents))
             logger.info(f"Including invoke_acp_agent tool ({len(acp_agents)} agent(s): {list(acp_agents.keys())})")