Added Oxibadge, a minimal Tauri + Svelte desktop client

Scaffolds the oxibadge crate/frontend as a new workspace member, stripped
down to a bare hello-world, and
extends the CI pipeline

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

oxibadge/src/routes/+page.svelte

@@ -0,0 +1,33 @@
+<main>
+  <img src="/logo.svg" alt="Oxibadge logo" class="logo" />
+  <h1>Hello, world!</h1>
+</main>
+
+<style>
+  :global(body) {
+    margin: 0;
+    color: #f6f6f6;
+    background-color: #2f2f2f;
+    font-family: Inter, Avenir, Helvetica, Arial, sans-serif;
+  }
+
+  main {
+    min-height: 100vh;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 1.5rem;
+  }
+
+  .logo {
+    width: 8rem;
+    height: 8rem;
+  }
+
+  h1 {
+    margin: 0;
+    font-size: 2rem;
+    font-weight: 500;
+  }
+</style>