feat: initial Tauri desktop shell for BatchTube v1.0

loading.html

@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<title>BatchTube — Starting...</title>
+<style>
+* { margin: 0; padding: 0; box-sizing: border-box; }
+body {
+  background: #0d0f14;
+  color: #e8eaf0;
+  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  height: 100vh;
+  gap: 24px;
+}
+.logo { font-size: 2.5rem; font-weight: 800; }
+.logo span { color: #FF8822; }
+.spinner {
+  width: 40px; height: 40px;
+  border: 3px solid rgba(255,136,34,0.2);
+  border-top-color: #FF8822;
+  border-radius: 50%;
+  animation: spin 0.8s linear infinite;
+}
+@keyframes spin { to { transform: rotate(360deg); } }
+.status { color: #8892a4; font-size: 0.9rem; }
+</style>
+</head>
+<body>
+<div class="logo">Batch<span>Tube</span></div>
+<div class="spinner"></div>
+<div class="status" id="status">Starting engine...</div>
+<script>
+async function checkServer() {
+  try {
+    const r = await fetch('http://localhost:8765/api/health');
+    if (r.ok) {
+      document.getElementById('status').textContent = 'Ready! Loading...'
+      window.location.href = 'http://localhost:8765';
+      return;
+    }
+  } catch(e) {}
+  setTimeout(checkServer, 500);
+}
+checkServer();
+</script>
+</body>
+</html>