Retire Tier A: delete the CI trend workflow, scripts, guards, and the published chart

[blooop]

Question

Build ticket (decided by #296): retire Tier A — the per-merge CI trend — in one slice.

Delete:

• .github/workflows/bench.yml
• scripts/bench_points.py, scripts/bench_cold_reset.sh
• test/test_bench_workflow.py, test/test_bench_points.py, test/test_bench_doc.py
• dev/bench/ on the gh-pages branch — a frozen chart that looks live is a trap; the 92 published points stay reachable in that branch's git history.

Keep (Tier B and C, per #296): scripts/bench_launch.py, test/fixtures/bench_harness.py, rust/devlaunch-core/src/timing.rs, the frozen stage names in public-api.txt.

One check the tier table glossed: test/test_bench_record_schema.py was tallied as Tier A, but it guards the record bench_launch.py --record writes — Tier B output. If its assertions bind the kept harness's record format, it stays; delete it only if they are trend-specific. Default: keep.

Docs ride along in the same PR: docs/performance.md (loses its doc-guard when test_bench_doc.py goes — rewrite its trend/chart sections to describe on-demand measurement via the local harness), the README's mention of the trend/chart if any, and CLAUDE.md's guard list (it names test_bench_doc.py reading docs/performance.md). Any bench-related pixi tasks that only fed the trend go too; bench itself (Tier B) stays.

Blocked by #502 — the e2e foreign-uid case lands first, so the #240-class coverage never lapses.

Worked via wf-tdd, reviewed via wf-review, per the map's Notes.