scripts: archive obsolete one-off shell/python scripts to legacy/ (D2, D3)

D2: run_benchmark.sh and run_experiments.sh still pass --time-scale and
--max-inflight-sessions to the replayer, but those flags were removed when
the project moved to trace-driven dispatch. The scripts cannot run as-is.

D3: ~25 ad-hoc analyze_* / compare_* / profile_* / final_* scripts and a
handful of single-experiment run_*.sh point at /home/admin/cpfs paths,
deleted output directories, or a sampled trace file that no longer exists.
Keep them in scripts/legacy/ for historical reference; the scripts that
remain in scripts/ (analyze_trace, analyze_breakdown, analyze_cache_hit,
analyze_eviction, compare_results, compute_roofline, sample_trace,
analyze_agentic_patterns, simulate_cache_policies, plus launch_*.sh,
gpu_monitor.sh, bench.sh) cover the current workflow.

Adds scripts/legacy/README.md to document the archival policy.

scripts/legacy/README.md

@@ -0,0 +1,20 @@
+# scripts/legacy
+
+One-shot scripts kept for historical reference. They were tied to specific
+experiments (cluster paths, deleted output dirs, removed CLI flags such as
+`--time-scale` / `--max-inflight-sessions`) and are no longer expected to
+run as-is.
+
+For new experiments use `scripts/bench.sh`. Pre-existing structured
+analyses still live in `scripts/` (e.g. `analyze_trace.py`,
+`analyze_breakdown.py`, `analyze_cache_hit.py`, `analyze_eviction.py`,
+`compare_results.py`, `compute_roofline.py`).
+
+If you need to revive a legacy script, expect to:
+
+- update hardcoded paths (cluster `/home/admin/cpfs/...`, deleted trace
+  files, missing `outputs/<exp>/...` directories);
+- adapt to the current replayer CLI (`--time-scale` and
+  `--max-inflight-sessions` were removed when methodology moved to
+  trace-driven dispatch);
+- re-verify the assumptions documented in `REPORT.md`.