feat(tests): screenshot regression + Discord review, perf-tracked

New tooling in tests/tools/screenshots/ (TypeScript via tsx):
- compare.ts: one pixelmatch engine (AA-excluded), connected-component
  "where to look" boxes, old|new+boxes|heatmap triptych, per-engine floors.
- promote.ts: churn-free updater — overwrite a baseline only when decoded
  pixels differ beyond the floor, copying CI bytes verbatim (no re-encode
  churn); pulls a CI run via `gh run download` or a local --from dir.
- post-discord.ts: always-on CI-on-main report (SHA + e2e status + the
  track-only runtime-perf table), then screenshot triptychs, batched +
  size-capped + flood-collapsed + 429-aware.
- perf-report.ts: perf table with Δ vs the previous main run (via gh).
- changelog.ts: no-build git-history baseline differ (Discord trigger B).
- noise.ts / gen-manifest.ts: calibration + manifest generation.

CI wiring:
- wasm-build.yml: post-test step runs the gate + report on the already-
  produced test-results (no extra build); report-only (continue-on-error),
  posts only on push to main, inert without DISCORD_WEBHOOK_URL.
- ci-ubicloud.yml: secrets: inherit (pass the webhook through).
- screenshot-changelog.yml: ~30s no-build changelog on baseline changes.

screenshot-manifest.json: canonical 354-name set + best-effort engine tags
(313 chromium-swiftshader / 41 firefox-llvmpipe).

Normalize scale:'device'->'css' across 18 spec files (no-op at CI DSF=1)
so committed baselines are uniformly css-scaled.

Design: CI's Linux render is the single source of truth; no pinned
container (accept rare env drift -> re-promote); dev commits via promote.
Replaces the byte-cmp compare-screenshots.sh + file-size-proxy
update-baseline-screenshots.sh (kept for now until the first re-baseline).

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

CLAUDE.md

@@ -6,8 +6,8 @@ A lot of native module have to be compiled to wasm, the most complex is wxwidget
 The e2e tests are in /tests, with a README and WHATWORKS md files
 The e2e tests are separated per feature
 Wxwidgets wasm port has hooks for finding positions of UI elements, tests use that
-The test have screenshots that are tracked with git, use compare-screenshots.sh to see what changed
-Update test images with /scripts/update-baseline-screenshots.sh when a new image is added
+The test screenshots are tracked with git; CI's Linux render is the source of truth (tooling: tests/tools/screenshots/, see its README).
+To update baselines, promote a CI run's render (churn-free — only meaningfully-changed images restage): `cd tests && npm run screenshots:promote -- --run <ci-run-id>`, then commit. `npm run screenshots:check` is the local gate; on each main push CI posts a screenshot-diff + runtime-perf report to Discord.
 The tests have log files in tests/logs/{wxwidgets/kicad}/{test-name} after each run where the js console and cpp logs are visible
 Always check screenshots for validating tests
 Run e2e tests from /tests folder: `npm run test:kicad` or `npm run test:e2e` (not playwright directly)