Better model download management

src/index.css

@@ -306,6 +306,29 @@ body {
   white-space: nowrap;
 }
 
+/* Explicit weight download for the selected model (D-020). */
+.model-download-button {
+  border: 1px solid var(--border);
+  background: transparent;
+  color: inherit;
+  border-radius: 999px;
+  padding: 0.1rem 0.7rem;
+  font-size: 0.75rem;
+  white-space: nowrap;
+  cursor: pointer;
+  transition: border-color 0.15s, color 0.15s;
+}
+
+.model-download-button:hover:enabled {
+  border-color: #3d6b4f;
+  color: #9ad6ae;
+}
+
+.model-download-button:disabled {
+  opacity: 0.6;
+  cursor: default;
+}
+
 /* --- PWA / offline (M3) --- */
 .offline-status {
   margin: 0.5rem 0 0.75rem;