Add LNbits attribution to sidebar footer

- Add "Powered by ⚡LNbits" link to both desktop and mobile sidebars
- Links to lnbits.com in new tab
- Includes separator divider above attribution

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/layout/AppSidebar.vue

@@ -129,6 +129,19 @@ const isActive = (href: string) => {
             Settings
           </router-link>
           -->
+
+          <!-- LNbits Attribution -->
+          <Separator class="my-2" />
+          <div class="text-center">
+            <a
+              href="https://lnbits.com"
+              target="_blank"
+              rel="noopener noreferrer"
+              class="text-xs text-muted-foreground hover:text-foreground transition-colors"
+            >
+              Powered by ⚡LNbits
+            </a>
+          </div>
         </li>
       </ul>
     </nav>

src/components/layout/MobileDrawer.vue

@@ -10,7 +10,7 @@ import {
   SheetTitle,
 } from '@/components/ui/sheet'
 import { Button } from '@/components/ui/button'
-// import { Separator } from '@/components/ui/separator' // TODO: Uncomment when Settings page is implemented
+import { Separator } from '@/components/ui/separator'
 import {
   Home,
   Calendar,
@@ -152,6 +152,19 @@ const navigateTo = (href: string) => {
             Settings
           </button>
           -->
+
+          <!-- LNbits Attribution -->
+          <Separator class="my-2" />
+          <div class="text-center">
+            <a
+              href="https://lnbits.com"
+              target="_blank"
+              rel="noopener noreferrer"
+              class="text-xs text-muted-foreground hover:text-foreground transition-colors"
+            >
+              Powered by ⚡LNbits
+            </a>
+          </div>
         </div>
       </div>
     </SheetContent>