refactor(backend): consolidate thread_id resolution into shared get_thread_id() utility (#2522)

Extract duplicated thread_id fallback logic from 11 files into a single
  deerflow.utils.runtime.get_thread_id() function with a documented 3-level
  cascade (runtime.context → runtime.config → get_config()).

  The module docstring also clarifies the __pregel_runtime injection pattern used in
  gateway mode.

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

@@ -28,6 +28,7 @@ from deerflow.skills.manager import (
     validate_skill_name,
 )
 from deerflow.skills.security_scanner import scan_skill_content
+from deerflow.utils.runtime import get_thread_id
 
 logger = logging.getLogger(__name__)
 
@@ -42,14 +43,6 @@ def _get_lock(name: str) -> asyncio.Lock:
     return lock
 
 
-def _get_thread_id(runtime: ToolRuntime[ContextT, ThreadState] | None) -> str | None:
-    if runtime is None:
-        return None
-    if runtime.context and runtime.context.get("thread_id"):
-        return runtime.context.get("thread_id")
-    return runtime.config.get("configurable", {}).get("thread_id")
-
-
 def _history_record(*, action: str, file_path: str, prev_content: str | None, new_content: str | None, thread_id: str | None, scanner: dict[str, Any]) -> dict[str, Any]:
     return {
         "action": action,
@@ -98,7 +91,7 @@ async def _skill_manage_impl(
     """
     name = validate_skill_name(name)
     lock = _get_lock(name)
-    thread_id = _get_thread_id(runtime)
+    thread_id = get_thread_id(runtime)
 
     async with lock:
         if action == "create":