Slate v2 Benchmark Layout Reorg

Goal

Replace the current flat benchmark-script sprawl with one cleaner benchmark home that is easier to extend without copying another script and hoping the flags line up.

Harsh Read

Current benchmark layout is functional but sloppy:

• benchmark files are flat in scripts/
• browser, compare, core, and react lanes are mixed together
• compare scripts duplicate repo/build/run plumbing
• browser scripts duplicate Playwright timing helpers
• there is no local README where someone can discover how to add a lane without archaeology

Desired End State

• one benchmark root under scripts/benchmarks/
• grouped by lane family, not by whatever was added first
• shared helpers for compare and browser harness code
• root package.json commands stay stable
• a local README explains:
  • folder structure
  • command naming
  • when to create a new lane
  • how to extend the shared helpers

Phases

1. Create benchmark root and family folders
2. Extract shared compare/browser helpers
3. Move existing benchmark files onto the new structure
4. Update package commands to the new paths
5. Add scripts/benchmarks/README.md
6. Run fresh verification on representative lanes