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

components/units/converter/SearchUnits.tsx

@@ -193,7 +193,7 @@ export default function SearchUnits({ onSelectUnit }: SearchUnitsProps) {
 
       {isOpen && query && results.length === 0 && (
         <div className="absolute z-50 w-full mt-2 bg-popover border rounded-lg shadow-lg p-4 text-center text-muted-foreground">
-          No units found for "{query}"
+          No units found for &quot;{query}&quot;
         </div>
       )}
     </div>