Trajectory time_cost always set to -1

[RENEK-bool]

I've discovered that the time_cost field in the trajectory table is always set to -1 due to hardcoding, which means actual execution time is not being recorded for trajectory entries. This prevents meaningful time-based analysis of agent performance.

After investigating the code, I found:
In TrajectoryModel.from_task_recorder() method (line 32 of utu/db/trajectory_model.py), time_cost is hardcoded to -1.

This seems to be an incomplete implementation where time recording functionality was intended but not fully implemented. The presence of the time_cost field suggests it was planned, but the actual measurement logic is missing.