feat: embeddable calculator widgets with postMessage resize (issue #121)

[yy1142274323]

Bounty #121 — Embeddable calculator widgets for external sites

Closes #121

Acceptance criteria

• Embed build for at least Blind Flange and Dished End calculators
  • New routes: /embed/blind-flange-calculator/ and /embed/pressure-vessel-dished-end-calc/
  • Verified compiled in the production build (build/embed/*/index.html both generated)
• postMessage-based resize handling; no third-party cookies required
  • EmbedUtilityPage measures the same-origin tool iframe content height, sizes the frame to it, and posts {source: 'cadautoscript-embed', type: 'resize', height, slug} to the embedding parent
  • The embed route sets no cookies and loads no third-party scripts
• Documentation page with copy-paste snippet
  • docs/utilities/embed-calculators.md rewritten: embed URL table, copy-paste iframe + parent-side resize-listener snippet for both calculators, how-it-works section
• "Powered by" backlink in the widget footer
  • Slim footer on every embed linking to the full calculator page

Implementation notes

• New shared component src/components/Utilities/EmbedUtilityPage.tsx (minimal chrome: no navbar/footer, just the tool iframe + powered-by bar)
• Two thin route files under src/pages/embed/<slug>.tsx (3 lines each, factory pattern — easy to extend to other calculators)
• Reuses the existing utilityPageConfigs (appPath, title, iframeAllow), so embed behavior stays in sync with the full shell pages
• Embed pages carry <meta name="robots" content="noindex"> to protect search visibility of the main pages
• pnpm build passes; embed routes present in the generated static output

Extending to more calculators

import {EmbedUtilityPage} from '@site/src/components/Utilities/EmbedUtilityPage';

export default EmbedUtilityPage('<slug>');

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[yy1142274323]

/claim #121

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