feat(landing): footer copy = About Velxio (replaces wrong MIT/avr8js line)

The previous footer credit ("MIT License · Powered by avr8js &
wokwi-elements") was wrong twice over: velxio is AGPLv3 (with a
commercial license available), and the project now ships much more
than the two libraries it singled out (rp2040js, eecircuit-engine,
QEMU, ESP-IDF, arduino-cli, Monaco editor, ...).

Replace it with a one-paragraph About Velxio that sits at the bottom
of the landing page, mirrors what the blog footer shows at
velxio.dev/blog/, and correctly states the AGPLv3 license.

Widen .footer-copy to max-width: 680px so the longer copy has room
to breathe and breaks across two lines on desktop.

frontend/src/pages/LandingPage.css

@@ -972,9 +972,11 @@
 }
 
 .footer-copy {
-  font-size: 11.5px;
+  font-size: 12px;
+  line-height: 1.7;
   color: var(--text-dim);
-  margin: 0;
+  margin: 0 auto;
+  max-width: 680px;
   width: 100%;
   text-align: center;
   font-family: var(--mono);

frontend/src/pages/LandingPage.tsx

@@ -1262,18 +1262,10 @@ export const LandingPage: React.FC = () => {
           <Link to="/about">About</Link>
         </div>
         <p className="footer-copy">
-          MIT License · Powered by{' '}
-          <a href="https://github.com/wokwi/avr8js" target="_blank" rel="noopener noreferrer">
-            avr8js
-          </a>{' '}
-          &amp;{' '}
-          <a
-            href="https://github.com/wokwi/wokwi-elements"
-            target="_blank"
-            rel="noopener noreferrer"
-          >
-            wokwi-elements
-          </a>
+          Velxio is a free, open-source circuit and microcontroller simulator
+          that runs entirely in your browser. Arduino, ESP32, RP2040 and
+          ATtiny85, with SPICE-accurate analog co-simulation. Built for
+          makers, students and embedded engineers learning by doing. AGPLv3.
         </p>
       </footer>
     </div>