Refactors the event layout and stacking logic based on review feedback.
This includes:
- Merging conflicting event groups to prevent inconsistencies.
- Implementing minimal stack level assignment using a min-heap.
- Consolidating styling and using DateService for drag operations.
- Adding reflow after drag and drop.
- Improving the column event filtering to include events overlapping midnight.
- Ensuring explicit sorting of events for grid layout.
Introduces a 3-phase algorithm in `EventStackManager` for dynamic event positioning. Groups events by start time proximity to determine optimal layout.
Optimizes horizontal space by using side-by-side grid columns for simultaneous events and allowing non-overlapping events to share stack levels. Supports nested stacking for late-arriving events within grid columns.
Includes comprehensive documentation (`STACKING_CONCEPT.md`) and a visual demonstration (`stacking-visualization.html`) to explain the new layout logic. Updates event rendering to utilize the new manager and adds extensive test coverage.
