eval: commit milestone bench output (track generated figures + results)

Per request, the milestone bench output is now tracked in git instead of
gitignored, so the figures/results are viewable on the remote:

- src/kernbench/benches/1H_milestone_output/gemm/  (3 PNGs + gemm_sweep.json)
- src/kernbench/benches/1H_milestone_output/ccl/   (3 per-topology PNGs,
  buffer-kind PNG+CSV, FSIM comparison PNG, topology.png, summary.csv)

Drop the .gitignore rule; update ADR-0054 D3 + Negative (EN+KO) to say the
output is committed (regenerable by rerunning the bench). Artifacts produced
by full bench runs (milestone-1h-gemm non-FAST, milestone-1h-ccl).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -6,9 +6,6 @@
 # Auto-generated mesh file
 cube_mesh.yaml
 
-# Milestone bench output (regenerable: kernbench run --bench milestone-1h-*)
-src/kernbench/benches/1H_milestone_output/
-
 # Python
 __pycache__/
 *.py[cod]