Optimize staggered grid layout to minimize whitespace gaps

[techeretic]

Summary

• Add SegmentOptimizer — a new utility that reorders items within each segment (groups of single-span items between full-span items) to minimize column height imbalance in the 2-column LazyVerticalStaggeredGrid
• Simulation-based hill climbing algorithm — simulates the grid's "shortest column first" placement, scores orderings by cumulative column height difference, and iteratively swaps items to find the optimal arrangement. Starts from an LPT (Longest Processing Time) initial solution for fast convergence
• Reduce grid spacing from 8dp to 4dp (content padding, horizontal arrangement, and vertical item spacing) for a tighter, denser layout

How it works

1. Full-span items reset both columns to equal height, creating natural "segments" of single-span items
2. For each segment (~5-15 items), the optimizer simulates how the grid places items and finds the ordering that keeps both columns as balanced as possible
3. The optimization runs once on the full dataset at initialization, so paginated pages serve already-optimized slices with zero runtime overhead

Files changed

File	Change
SegmentOptimizer.kt	New — segment extraction, gap scoring simulation, hill climbing optimizer
GridItemRepository.kt	Wrap dataset with SegmentOptimizer.optimize()
StaggeredGridScreen.kt	Reduce grid spacing from 8dp to 4dp

Test plan

• Verify app builds and installs without errors
• Scroll through the grid and confirm columns are visually balanced with minimal whitespace
• Verify full-span items still appear correctly with 5+ single items between them
• Verify pagination and loading indicators work as before
• Test both Fast and Slow network speeds

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