完善部分平台治理功能，及修改看板缺陷

backend/tests/test_governance.py

@@ -138,6 +138,14 @@ class FakePlatformStore:
                     return dict(u)
         return None
 
+    def create_session(self, user_id: str) -> dict[str, Any]:
+        import secrets
+        sid = secrets.token_hex(16)
+        return {"session_id": sid, "user_id": user_id}
+
+    def finish_session(self, session_id: str) -> None:
+        pass
+
     def users(self) -> list[dict[str, Any]]:
         return [dict(u) for u in self._users]
 
@@ -392,12 +400,21 @@ class FakePlatformStore:
     def tasks(self) -> list[dict[str, Any]]:
         return self._tasks
 
+    def eval_tasks(self) -> list[dict[str, Any]]:
+        return []
+
     def compute_nodes(self) -> list[dict[str, Any]]:
         return self._compute_nodes
 
     def gpus(self) -> list[dict[str, Any]]:
         return self._gpus
 
+    def compare_tasks(self) -> list[dict[str, Any]]:
+        return []
+
+    def trained_models(self) -> list[dict[str, Any]]:
+        return []
+
     def system_info(self) -> dict[str, Any]:
         return {"cpu": {}, "memory": {}}