test(perf): track-only runtime-perf E2E for eeschema + pcbnew

Measures the current build's cold load, open+render, and pan/zoom FPS
(1x/4x/6x CPU-throttle sweep) for both editors, writing
tests/test-results/perf-*.json. Track-only: asserts only that the app booted
and the document opened — no perf thresholds, so it never gates CI.

Runs on a new Chromium `perf` Playwright project (CDP throttling; pcbnew needs
V8 anyway) via `npm run test:perf`, and is wired into wasm-build.yml as a
continue-on-error step so the numbers are captured/uploaded without flaking the
gate. Reuses the existing fixtures, ready-signal, fs-inject, and board-ready
helpers; FPS counter is cancel-able so a throttle sweep on one page doesn't
accumulate rAF loops.

.gitignore: ignore /benchmark-builds/ (disposable prebuilt-WASM + standalone
harness bundle used to reproduce the native-vs-JS-EH comparison locally).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/package.json

@@ -18,6 +18,7 @@
     "test:kicad": "npm run test:kicad:firefox",
     "test:kicad:ci": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=firefox --project=chromium-ci",
     "test:kicad:headed": "npm run test:kicad:chrome",
+    "test:perf": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=perf --workers=1",
     "test:pcbnew:firefox": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=firefox kicad/pcbnew.spec.ts",
     "test:pcbnew:chrome": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=chromium --headed kicad/pcbnew.spec.ts",
     "test:eeschema:firefox": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=firefox kicad/eeschema.spec.ts",