feat: enhance accessibility and styling across the application with s…

[devaraj3]

What changed

1. Code-split the CAD viewer away from non-viewer routes (main fix)

• App (the full CAD viewer engine — Three.js, OpenCascade WASM wiring) was statically imported in main.tsx, the shared entry point for every route. Even though /viewer wraps it in <ClientOnly>, that only prevents server-rendering — the browser was still downloading and parsing the entire viewer bundle on the landing page and guide pages, which never use it at all.
• Fixed via React.lazy(() => import("./ui/App")) + <Suspense>, so it's now a separate chunk only fetched when someone actually navigates to /viewer
• Confirmed via build output: one monolithic 1,625 KB bundle → 372 KB shared chunk + 1,250 KB viewer-only chunk, verified via network capture that / and /guides/split-step-assembly no longer fetch the viewer chunk or its WASM worker at all

2. Fixed insufficient button contrast

• Flagged by PageSpeed's accessibility audit: white text on #3b82f6 measured 3.68:1, failing WCAG AA (needs 4.5:1)
• Changed idle state to #2563eb (5.17:1, passes), #1d4ed8 on hover — applied to both the landing page CTA and the viewer header's Upload button

3. Added <main> landmark

• Missing on Landing and the guide page (the viewer already had one) — added for screen-reader navigation

4. Fixed llms.txt link formatting

• The Guides and Live app entries weren't using proper markdown link syntax, which PageSpeed's Agentic Browsing check flagged as "does not appear to contain any links" — converted to [text](url) format

Why

• Google's PageSpeed Insights flagged a 5,110ms Total Blocking Time on the landing page — meaning the page looked ready at 0.9s but was actually unresponsive to input for 5+ seconds while the (unused, on that page) viewer bundle parsed in the background. This is both a real visitor-facing UX problem and a genuine Core Web Vitals ranking factor
• The other three fixes were concrete, specific issues from the same report, not speculative changes

Validation

• Build output confirms separate chunks; network capture confirms non-viewer routes don't fetch the viewer bundle
• /viewer loaded and fully tested: file upload, orbit, Measure, Wireframe toggle, view-cube (FRONT face confirmed) all functional after lazy-loading
• Full regression matrix (STEP single/assembly, IGES, STL, OBJ) — zero console errors
• typecheck and lint clean
• Contrast ratio verified numerically (5.17:1, passes AA) — not just visually judged
• Live PageSpeed Insights re-run on the deployed site, to get a real, comparable Total Blocking Time number (local Lighthouse numbers use different hardware/scaling than PSI's cloud runner, so they're directionally correct but not the same absolute figure)

Notes

• The wireframe density sliders remain intentionally hidden (SHOW_WIREFRAME_DENSITY_CONTROLS = false) — unrelated pre-existing state, not touched by this work

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Project	Deployment	Actions	Updated (UTC)
cad-viewer	Ready	Preview	Aug 7, 2026 6:57am