Fix D-InSAR export UI and task folder isolation

frontend/src/App.css

@@ -3709,6 +3709,12 @@ input[type="checkbox"] {
   gap: 6px;
   cursor: pointer;
 }
+.export-select-hint {
+  margin-bottom: 8px;
+  font-size: 12px;
+  color: var(--color-text-secondary);
+  line-height: 1.5;
+}
 .export-result-list {
   list-style: none;
   padding: 0;
@@ -3780,15 +3786,28 @@ input[type="checkbox"] {
   padding-top: 12px;
   border-top: 1px solid var(--color-border);
 }
-.result-export-modal .modal-footer .btn-primary {
-  background: var(--color-primary);
-  color: white;
-  border: none;
+.result-export-modal .modal-footer button {
+  min-width: 108px;
   padding: 6px 16px;
   border-radius: 4px;
+  border: 1px solid var(--color-border);
+  background: #fff;
+  color: var(--color-text-primary);
   cursor: pointer;
 }
-.result-export-modal .modal-footer .btn-primary:disabled {
+.result-export-modal .modal-footer .btn-secondary:hover:not(:disabled) {
+  background: var(--color-panel-muted);
+}
+.result-export-modal .modal-footer .btn-primary {
+  background: var(--color-accent);
+  color: #fff;
+  border: none;
+  font-weight: 600;
+}
+.result-export-modal .modal-footer .btn-primary:hover:not(:disabled) {
+  background: var(--color-accent-strong);
+}
+.result-export-modal .modal-footer button:disabled {
   opacity: 0.5;
   cursor: not-allowed;
 }