fix: render Add passkey button on empty state

The Empty component ignores children, so the button was silently dropped
when using <Empty> as an htm wrapper. Inline the card structure instead.

webui/static/pages/passkeys.js

@@ -228,12 +228,13 @@ function CredentialsPage() {
                     Add passkey
                 </button>`,
             }),
-            html`<Empty text="No passkeys registered">
+            html`<div class="card" key="empty">
+                <div class="text-muted text-sm">No passkeys registered</div>
                 <button class="btn btn-sm btn-primary"
                     onClick=${() => webauthnSupported() && addCredentialModal()}>
                     Add passkey
                 </button>
-            </Empty>`,
+            </div>`,
         ];
     }