design: improve UI consistency and footer layout

- Update text sizing to text-base throughout for consistency
- Improve arrow icon visibility (gray-400 → gray-200 on hover)
- Reorganize tool badges: Open Source first, specialty second, Free third
- Update badge labels: Vert (Converter), Stirling (PDF), Units/Figlet (Open Source)
- Redesign footer: single-row layout with brand pill, centered copyright, GitHub link
- Update footer border: lighter gray-600, constrained to content width

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/Stats.tsx

@@ -57,7 +57,7 @@ export default function Stats() {
               <div className="text-4xl font-bold mb-2 bg-clip-text text-transparent bg-gradient-to-r from-purple-400 to-cyan-400">
                 {stat.number}
               </div>
-              <div className="text-gray-400 text-sm font-medium">
+              <div className="text-gray-400 text-base font-medium">
                 {stat.label}
               </div>
             </motion.div>