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/InvoicePreview.js

@@ -335,7 +335,7 @@ const InvoicePreview = () => {
                 <div className="flex items-center gap-3">
                   <FileText className="h-5 w-5 text-blue-600 dark:text-blue-400" />
                   <h2 className="text-lg font-semibold text-gray-900 dark:text-white">Invoice Preview</h2>
-                  <div className="hidden sm:flex items-center gap-2 text-sm text-gray-500 dark:text-gray-400">
+                  <div className="hidden sm:flex items-center gap-2 text-sm text-gray-600 dark:text-gray-600">
                     <span>•</span>
                     <span>{pdfPageSize} Format</span>
                   </div>