chore(hub): add "Powered by ⚡ LNbits" footer

Small subtitle above the bottom dock, links to https://lnbits.com
in a new tab. Same muted styling as the existing tile sub-labels.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/Hub.vue

@@ -143,6 +143,16 @@ function notImplemented() {
           </span>
         </component>
       </div>
+
+      <p class="text-[10px] text-center text-muted-foreground/70 mt-2">
+        Powered by
+        <a
+          href="https://lnbits.com"
+          target="_blank"
+          rel="noopener noreferrer"
+          class="hover:text-foreground transition-colors"
+        >⚡ LNbits</a>
+      </p>
     </div>
 
     <!-- Bottom bar: profile & user preferences -->