feat(web): marketing Home page and the product component library (ADR 0023)

Product UI components are built once at design size from the Figma file and reused by the marketing mockups and, later, the app. Text contrast tokens now meet WCAG AA in both themes, with a test. Pricing stays hidden until decided.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014SdXCbrN5PtGExkpvMaMHx

web/public/icons/shield-check.svg

@@ -0,0 +1,6 @@
+<svg preserveAspectRatio="none" overflow="visible" style="display: block;" width="14" height="14" viewBox="0 0 14 14" fill="none" xmlns="http://www.w3.org/2000/svg">
+<g id="Icon/shield-check">
+<path id="Vector" d="M11.6667 7.58333C11.6667 10.5 9.625 11.9583 7.19833 12.8042C7.07126 12.8472 6.93323 12.8452 6.8075 12.7983C4.375 11.9583 2.33333 10.5 2.33333 7.58333V3.5C2.33333 3.34529 2.39479 3.19692 2.50419 3.08752C2.61358 2.97813 2.76196 2.91667 2.91667 2.91667C4.08333 2.91667 5.54167 2.21667 6.55667 1.33C6.68025 1.22442 6.83746 1.1664 7 1.1664C7.16254 1.1664 7.31975 1.22442 7.44333 1.33C8.46417 2.2225 9.91667 2.91667 11.0833 2.91667C11.238 2.91667 11.3864 2.97813 11.4958 3.08752C11.6052 3.19692 11.6667 3.34529 11.6667 3.5V7.58333Z" stroke="#1F6B42" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
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+</g>
+</svg>