Summary

This PR turns the detector work into a much more explicit architecture, with the speed and inspection tooling needed to keep improving it safely.

Detector architecture

• Refactors the old detector monolith into focused modules for the registry, shared utilities, pure rule checks, profiling, CLI wiring, source/regex scans, static HTML/CSS scans, browser URL scans, injected browser runtime, and screenshot-based visual contrast.
• Keeps the public API facade intact through cli/engine/detect-antipatterns.mjs while moving implementation into cli/engine/engines/*, cli/engine/rules/*, cli/engine/shared/*, and cli/engine/browser/injected/*.
• Updates browser and extension builds to generate from the browser injected entry instead of stripping Node sections out of the old universal file.
• Moves build-time rule metadata reads to the detector registry instead of scraping the monolithic source file.

Static HTML/CSS engine

• Replaces the local HTML detection path with a fast static HTML/CSS parser stack: htmlparser2, css-select, css-tree, and domutils.
• Removes the jsdom-based path and keeps static analysis intentionally layout-free.
• Preserves detector-needed cascade behavior: linked local stylesheets, @layer flattening, selector matching, specificity/source order, !important, inline styles, variables/fallbacks, inherited typography properties, and needed shorthand expansion.

Browser, visual contrast, and extension behavior

• Adds createBrowserDetector() for warm browser reuse while keeping one-shot detectUrl() compatibility.
• Splits pure detection from overlay rendering with window.impeccableDetect() / window.impeccableDetectAsync() and window.impeccableScan() / window.impeccableScanAsync().
• Adds browser-first visual contrast analysis and pixel-diff screenshot fallback for hard cases like image backgrounds.
• Adds lazy in-browser visual contrast resolution for offscreen candidates and keeps extension-mode async visual contrast errors visible to the panel.

Benchmarks and detector lab

• Adds scripts/benchmark-detector.mjs plus bench:detector and bench:detector:browser scripts.
• Reports per-engine, per-phase, per-rule, per-target timing through the new profiling API.
• Adds the internal /detector workbench for navigating antipattern fixtures, running scans in an iframe, viewing findings, and seeing timing at a glance.
• Keeps benchmark output observational only; no hard budgets yet.

Validation

• bun run test
• bun run build:browser
• bun run build:extension
• bun run build:skills
• bun run build:site
• bun run bench:detector -- --quick
• bun run bench:detector:browser -- --quick
• git diff --check

Notes

• Local validation was run outside the sandbox where needed for Puppeteer/headless Chromium and repo build workflows.
• Rust/Go remains deferred; this branch focuses first on architecture, browser lifecycle, static parser reliability, visual contrast correctness, and measurable performance.