Add computeGridSize helper in call.ts that computes optimal row/column
counts for a video tile grid given tile count and container dimensions,
maximizing tile size while maintaining ~16:9 cells.
Apply via computed grid-template-columns/rows on the multi-grid path
(no-spotlight) in VideoCallContent.svelte, replacing the fixed
grid-cols-1 / grid-cols-1 sm:grid-cols-2 heuristic. The multi-grid now
handles all tile counts from 1 to 12+ smoothly.
- computeGridSize(tileCount, containerWidth, containerHeight) -> GridSize
- Container dimensions bound via clientWidth/clientHeight
- useMultiGrid: dropped the > 2 check, now !useSpotlightLayout
- gridStyle: computed grid-template-columns/rows string from gridSize
- Scope: multi-grid only, no spotlight/strip/breakpoint changes
