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>

.gitignore

@@ -1,5 +1,7 @@
 # DeerFlow docker image cache
 docker/.cache/
+# oh-my-claudecode state
+.omc/
 # OS generated files
 .DS_Store
 *.local