refactor: enhanced structure

frontend/src/assets/app.css

@@ -0,0 +1,27 @@
+:root {
+  /* CSS variables from theme.js would be injected here */
+  --bg-primary: #1c1c1c;
+  --bg-secondary: #121212;
+  /* ... all other theme variables */
+}
+
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+body {
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+  background-color: var(--bg-primary);
+  color: var(--text-primary);
+  touch-action: manipulation;
+  user-select: none;
+  -webkit-user-select: none;
+  -moz-user-select: none;
+  -ms-user-select: none;
+}
+
+/* Utility classes */
+.text-dim { color: var(--text-dim); }
+.text-secondary { color: var(--text-secondary); }