feat: WCAG AA accessibility, code splitting, responsive ads layout

- Add React.lazy code splitting for all 15 tool pages
- Fix WCAG AA contrast issues (304 text color fixes)
- Add ARIA labels and aria-expanded to navigation buttons
- Add aria-live for error announcements in tools
- Implement responsive ad layout:
  - Desktop (≥1280px): Right sidebar with 3 ad units
  - Tablet (1024-1279px): Bottom section with 3 horizontal units
  - Mobile (<1024px): Fixed bottom banner
- Add TabletAdSection component for tablet ad placement
- Integrate Onidel affiliate partnership
- Update all Adsterra domains to solutionbiologyisle.com
- Add release notes for 2026-02-18 updates

src/components/TabletAdSection.js

@@ -0,0 +1,27 @@
+import React from 'react';
+import AdBlock from './AdBlock';
+import OfferBlock from './OfferBlock';
+import AffiliateBlock from './AffiliateBlock';
+
+const TabletAdSection = () => {
+  return (
+    <div className="hidden lg:flex xl:hidden flex-col mt-8 pt-6 border-t border-gray-200 dark:border-gray-700">
+      <h3 className="text-sm font-medium text-gray-600 dark:text-gray-600 mb-4 text-center">
+        Sponsored
+      </h3>
+      <div className="flex justify-center gap-4 overflow-x-auto pb-4">
+        <div className="flex-shrink-0">
+          <AdBlock adKey="7c55aebcdd74f6e9a8dc24bd13e7d949" adDomain="solutionbiologyisle.com" />
+        </div>
+        <div className="flex-shrink-0">
+          <OfferBlock />
+        </div>
+        <div className="flex-shrink-0">
+          <AffiliateBlock />
+        </div>
+      </div>
+    </div>
+  );
+};
+
+export default TabletAdSection;