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/pages/PrivacyPolicy.js

@@ -252,7 +252,7 @@ const PrivacyPolicy = () => {
 
         {/* Footer */}
         <div className="mt-8 text-center">
-          <p className="text-sm text-slate-500 dark:text-slate-400">
+          <p className="text-sm text-slate-600 dark:text-slate-600">
             © {SITE_CONFIG.year} {SITE_CONFIG.title} • Your privacy is our priority
           </p>
         </div>