Add responsive desktop layout with left sidebar navigation

Desktop (≥1024px):
- Tab bar becomes a 220px left sidebar with brand name and nav items
- Page content shifts right and max-width constrained to 1200px
- Base font-size reset to 16px for readable text
- AI assistant floating button stays in bottom-right corner
- No change to mobile layout (bottom tab bar preserved)

uni-app/src/App.vue

@@ -26,4 +26,37 @@ uni-page-body {
   overflow-y: auto !important;
   min-height: 100% !important;
 }
+
+/* ===== Desktop responsive (≥1024px) ===== */
+@media (min-width: 1024px) {
+  /* Sidebar — shift page content right */
+  uni-page-body {
+    margin-left: 220px !important;
+    font-size: 16px !important;
+  }
+
+  /* Constrain + center page content */
+  uni-page-body > view {
+    max-width: 1200px !important;
+    margin-left: auto !important;
+    margin-right: auto !important;
+    padding: 40px 48px !important;
+  }
+
+  /* Cards more breathing room */
+  uni-page-body .card {
+    padding: 32px !important;
+    border-radius: 20px !important;
+  }
+
+  /* Fix floating AI assistant (clear sidebar + reasonable position) */
+  .ai-float-btn {
+    right: 40px !important;
+    bottom: 40px !important;
+  }
+  .ai-dialog {
+    right: 40px !important;
+    bottom: 100px !important;
+  }
+}
 </style>