(This question is a variation of the LeetCode question 986. Interval List Intersections. If you haven't completed that question yet, it is recommended to solve it first.)

A surveillance camera produces a chronologically ordered time series of readings, where each reading captures a timestamp and a motion intensity value. Given the readings and a sensitivity threshold, find all contiguous time periods during which the camera's motion intensity is at or above the threshold.

A motion period starts at the first reading that meets or exceeds threshold and ends at the last one in the unbroken run, regardless of gaps between adjacent timestamps. Both endpoints are inclusive, so a single qualifying reading produces a valid period [t, t].

Given two parallel arrays times and intensities and a threshold, return all motion periods as [start, end] pairs sorted by start time. Return an empty array if no reading meets the threshold.