Bench/context sweep snapshot

[huangzhenhua111]

What

• Add env-gated matmul shape aggregation (MLLM_MATMUL_SHAPE_LOG) to report top GEMM/SGEMM shapes by estimated FLOPs.

• Add sweep_context_v2.sh to run context sweep (prefill TTFT + decode-heavy).

• Add snapshot generator script (make_snapshot_nopandas.py) and ship a ready-to-share snapshot bundle:

  • raw CSV (bench_artifacts/data/*.csv)
  • plots (bench_artifacts/plots/*.png)
  • 1-page summary (bench_artifacts/snapshot.md)
  • reproduction guide (bench_artifacts/README.md)

Why

• Provide a minimal “one-click bench + stable CSV + at least one memory metric (peak RSS + KV estimate)” deliverable for the monthly package.
• Make bottlenecks measurable (tinyBLAS small-tile GEMM dominates; shapes are now visible).

How to reproduce

• Tested on x86_64 (WSL/Ubuntu), CPU backend
• See bench_artifacts/README.md.