bench: JSPI vs asyncify A/B — harness + results

Adds pcbnew-large-perf.spec.ts (PERF_LARGE-gated: repeated cold loads,
vme-wren/jetson opens, rAF + distinct-glcanvas-frame FPS under throttle,
wasm/JS heap checkpoints), fetchIntoMemfs + openAndWait/sampleMemory/
measureFpsDetailed perf-utils, dual 9.99+10.0 config seeding in pcbnew.html
so foreign-branch builds boot wizard-free, and the full benchmark report +
raw data under docs/features/async/migration-evidence/.

Headlines: wasm 94 vs 113 MB raw (18.6 vs 36.7 MB gzip), post-link tail
1.6 s/49 MB vs 63 s/6.1 GB per build, cold load −40 %, 27.7 MB board open
−45 %, real redraws +68 % at 4× throttle, boot heap −31 %.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016X9eh1s5sTx1o9Em9KBuwR

docs/features/async/23-jspi-runtime.md

@@ -216,6 +216,10 @@ same-origin serving works. Not fixed in the cleanup — tracked here.
 
 ## 10. Migration evidence
 
+- **A/B benchmark vs the asyncify build** (2026-08-14): build time / build
+  memory / bundle size / load / open / FPS / heap —
+  [`migration-evidence/jspi-vs-asyncify-bench-2026-08.md`](migration-evidence/jspi-vs-asyncify-bench-2026-08.md)
+  (raw data in `migration-evidence/bench-data-2026-08/`).
 - **Workflow results**: `migration-evidence/wf-result-11.json` /
   `wf-result-12.json` (the durable spike output; the rest of the
   `.jspi-assets/` spike tree was scratch and is gone — its ignore rule came