v3.57.0 — uiforge-visualgate (pixel-diff fidelity oracle)

Zero-dep pixel-diff gate: render two targets (url / .html / .png / project dir) and diff them via Playwright + canvas, reporting mismatch %% and the worst-differing region's bounding box so the restore loop can localize what to fix. Waits for webfonts to load/swap, serves a built dist/ or static dir, writes a diff image. This is the oracle that proves a restore is pixel-identical to the original instead of hoping it — it's how v3.56.0 was validated to 0% on shadcn.