Merge Overlapping Intervals

A data pipeline deduplicates overlapping maintenance windows and time-range records before writing them to a scheduling system. Given an array of intervals, merge all overlapping intervals and return a list of non-overlapping intervals that cover all the input ranges. **Input:** `intervals` — a list of `[start, end]` intervals (integers, `start <= end`). **Output:** A list of merged non-overlapping intervals, sorted by start value. **Key Rules:** - Two intervals are considered overlapping if one's start is ≤ the other's end. - Intervals touching at a single point (e.g., `[1,3]` and `[3,5]`) should be merged into `[1,5]`.