perf: responsive AVIF/WebP images; a11y contrast and link-text fixes

- scripts/optimize-images.mjs generates hashed AVIF/WebP variants at build time (sharp)
- Picture.astro + rehype plugin serve them via <picture> with srcset/sizes; hero gets fetchpriority=high
- footer CTA and active service-nav item meet WCAG AA contrast
- homepage Learn More link gets screen-reader-only context
- llms.txt: insights described as coming soon

package.json

@@ -4,9 +4,10 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev": "ASTRO_TELEMETRY_DISABLED=1 astro dev --host 0.0.0.0",
-    "build": "ASTRO_TELEMETRY_DISABLED=1 astro check && ASTRO_TELEMETRY_DISABLED=1 astro build",
+    "dev": "npm run images && ASTRO_TELEMETRY_DISABLED=1 astro dev --host 0.0.0.0",
+    "build": "npm run images && ASTRO_TELEMETRY_DISABLED=1 astro check && ASTRO_TELEMETRY_DISABLED=1 astro build",
     "preview": "ASTRO_TELEMETRY_DISABLED=1 astro preview --host 0.0.0.0",
+    "images": "node scripts/optimize-images.mjs",
     "typecheck": "ASTRO_TELEMETRY_DISABLED=1 astro check",
     "lint": "ASTRO_TELEMETRY_DISABLED=1 astro check",
     "seo:lint": "node scripts/seo-lint.mjs",
@@ -26,6 +27,7 @@
     "@astrojs/check": "^0.9.4",
     "@playwright/test": "^1.60.0",
     "prettier": "^3.5.3",
+    "sharp": "0.34.5",
     "typescript": "^5.8.3"
   }
 }