refactor: Remove all legacy variant-* class usage from Svelte components, enforce preset-* (Skeleton v4) everywhere

src/lib/element_qr_scanner_v2.svelte

@@ -404,7 +404,7 @@
                 on:click={ () => {
                     html5_qr_code.start({ facingMode: { exact: "environment"} }, config, qrCodeSuccessCallback);
                 }}
-                class="ae_btn__resume btn btn-sm variant-soft-primary">
+                class="ae_btn__resume btn btn-sm preset-tonal-primary">
                 <span class="fas fa-play"></span>
                 Resume
             </button> -->

src/lib/element_qr_scanner_v3.svelte

@@ -133,7 +133,7 @@
             <p class="text-sm text-error-400 font-semibold leading-snug">{error_msg}</p>
             <button
                 type="button"
-                class="btn btn-sm variant-filled-primary"
+                class="btn btn-sm preset-filled-primary"
                 onclick={start_scanning}
             >
                 Try Again