fix: resolve linting errors and improve ESLint configuration

- Downgrade ESLint to v9 to avoid circular structure errors in v10 config validation
- Downgrade eslint-config-next to v15 for stability
- Configure eslint.config.mjs with FlatCompat and appropriate ignores (.next, out)
- Escape entities in ColorBlindPage and SearchUnits to fix react/no-unescaped-entities
- Use useMemo for debounced function in FigletConverter to fix react-hooks/exhaustive-deps

app/(app)/pastel/accessibility/colorblind/page.tsx

@@ -194,7 +194,7 @@ export default function ColorBlindPage() {
                     Accessibility Tip
                   </h3>
                   <p className="text-sm text-muted-foreground">
-                    Ensure important information isn't conveyed by color alone. Use text
+                    Ensure important information isn&apos;t conveyed by color alone. Use text
                     labels, patterns, or icons to make your design accessible to everyone
                   </p>
                 </div>