feat: add configurable log level and token usage tracking (#1301)

* feat: add configurable log level and token usage tracking

- Add `log_level` config to control deerflow module log level, synced
  to LangGraph Server via serve.sh `--server-log-level`
- Add `token_usage.enabled` config with TokenUsageMiddleware that logs
  input/output/total tokens per LLM call from usage_metadata
- Add .omc/ to .gitignore

* fix: use info level for token usage logs since feature has its own toggle

* fix: sort imports to pass lint check

---------

Co-authored-by: greatmengqi <chenmengqi.0376@bytedance.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/packages/harness/deerflow/agents/lead_agent/agent.py

@@ -11,6 +11,7 @@ from deerflow.agents.middlewares.memory_middleware import MemoryMiddleware
 from deerflow.agents.middlewares.subagent_limit_middleware import SubagentLimitMiddleware
 from deerflow.agents.middlewares.title_middleware import TitleMiddleware
 from deerflow.agents.middlewares.todo_middleware import TodoMiddleware
+from deerflow.agents.middlewares.token_usage_middleware import TokenUsageMiddleware
 from deerflow.agents.middlewares.tool_error_handling_middleware import build_lead_runtime_middlewares
 from deerflow.agents.middlewares.view_image_middleware import ViewImageMiddleware
 from deerflow.agents.thread_state import ThreadState
@@ -227,6 +228,10 @@ def _build_middlewares(config: RunnableConfig, model_name: str | None, agent_nam
     if todo_list_middleware is not None:
         middlewares.append(todo_list_middleware)
 
+    # Add TokenUsageMiddleware when token_usage tracking is enabled
+    if get_app_config().token_usage.enabled:
+        middlewares.append(TokenUsageMiddleware())
+
     # Add TitleMiddleware
     middlewares.append(TitleMiddleware())
 
@@ -243,6 +248,7 @@ def _build_middlewares(config: RunnableConfig, model_name: str | None, agent_nam
     # Add DeferredToolFilterMiddleware to hide deferred tool schemas from model binding
     if app_config.tool_search.enabled:
         from deerflow.agents.middlewares.deferred_tool_filter_middleware import DeferredToolFilterMiddleware
+
         middlewares.append(DeferredToolFilterMiddleware())
 
     # Add SubagentLimitMiddleware to truncate excess parallel task calls