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/migration-evidence/bench-data-2026-08/build-summary-jspi.csv

@@ -0,0 +1,6 @@
+B-S1a,379,0,20131172352
+B-S1b,154,0,20515237888
+B-S2a,122,0,20695916544
+B-S2b,95,0,20612022272
+B-S3,26,2,4479885312
+B-S3,305,0,20694478848