add open source link to footer, rewrite README

- Added GitHub link in footer with 'Open source — star us on GitHub'
- Completely rewrote README with proper project documentation:
  - Features, format support tables, installation guides
  - CLI keybindings reference
  - Development setup and tech stack
  - Contributing guidelines and links

src/app/page.tsx

@@ -1143,9 +1143,20 @@ export default function LandingPage() {
 
       {/* ──── FOOTER ──── */}
       <footer className="text-center px-6 py-12 text-sm text-text-light">
-        <p>
+        <p className="mb-3">
           Built with love, runs on your machine.
         </p>
+        <a
+          href="https://github.com/noauf/Transmute"
+          target="_blank"
+          rel="noopener noreferrer"
+          className="inline-flex items-center gap-1.5 text-text-mid hover:text-text-dark transition-colors"
+        >
+          <svg width="16" height="16" viewBox="0 0 24 24" fill="currentColor" className="text-text-light">
+            <path d="M12 0c-6.626 0-12 5.373-12 12 0 5.302 3.438 9.8 8.207 11.387.599.111.793-.261.793-.577v-2.234c-3.338.726-4.033-1.416-4.033-1.416-.546-1.387-1.333-1.756-1.333-1.756-1.089-.745.083-.729.083-.729 1.205.084 1.839 1.237 1.839 1.237 1.07 1.834 2.807 1.304 3.492.997.107-.775.418-1.305.762-1.604-2.665-.305-5.467-1.334-5.467-5.931 0-1.311.469-2.381 1.236-3.221-.124-.303-.535-1.524.117-3.176 0 0 1.008-.322 3.301 1.23.957-.266 1.983-.399 3.003-.404 1.02.005 2.047.138 3.006.404 2.291-1.552 3.297-1.23 3.297-1.23.653 1.653.242 2.874.118 3.176.77.84 1.235 1.911 1.235 3.221 0 4.609-2.807 5.624-5.479 5.921.43.372.823 1.102.823 2.222v3.293c0 .319.192.694.801.576 4.765-1.589 8.199-6.086 8.199-11.386 0-6.627-5.373-12-12-12z"/>
+          </svg>
+          Open source — star us on GitHub
+        </a>
       </footer>
     </div>
   );