Add Better Benchmark performance summary dashboard (#8600)

## Summary

Adds a summary view for Better Benchmark results in PyTorch HUD.

- Shows overall model and kernel performance using geomean, median,
mean, and comparable-record counts.
- Breaks results down by suite and mode.
- Shows the largest model and kernel gains/regressions, ranked by
absolute latency impact.
- Displays comparison coverage and exclusion reasons.
- Links workflow IDs to their GitHub Actions runs.
- Uses lower-is-better green/red semantics with a neutral threshold for
small changes.
- Adds a dedicated backend query path for Better Benchmark summary data.

The benchmark records are produced by
pytorch/pytorch#193991

## Test plan

- [x] `yarn tsc --noEmit`
- [x] Prettier check for changed files
- [x] ESLint for changed files
- [x] Better Benchmark summary Jest tests
- [x] Validate parsing of kernel, projected-model, coverage, and
exclusion records
- [x] Validate suite/mode aggregation and mover ranking
- [x] Validate against uploaded B200 benchmark output

Author: karthickai