feat: improve accessibility and SEO (100/100 Lighthouse score)

Fixes color contrast, canonical URLs, viewport scaling, semantic lists,

and resolves 404 errors for manifest/imgproxy.

package.json

@@ -96,6 +96,7 @@
     "check:og": "tsx scripts/check-og-images.ts",
     "check:mdx": "node scripts/validate-mdx.mjs",
     "check:a11y": "start-server-and-test start http://localhost:3000 'pa11y-ci'",
+    "check:wcag": "tsx ./scripts/wcag-sitemap.ts",
     "cms:branding:local": "DIRECTUS_URL=${DIRECTUS_URL:-http://cms.klz.localhost} npx tsx --env-file=.env scripts/setup-directus-branding.ts",
     "cms:branding:testing": "DIRECTUS_URL=https://cms.testing.klz-cables.com npx tsx --env-file=.env scripts/setup-directus-branding.ts",
     "cms:branding:staging": "DIRECTUS_URL=https://cms.staging.klz-cables.com npx tsx --env-file=.env scripts/setup-directus-branding.ts",