fix: prevent planning mode dialog from overflowing viewport

Remove min-height: 300px from .planning-loading and add overflow: hidden
to .planning-initial so the modal stays within 80vh bounds.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

packages/dashboard/app/styles.css

@@ -12229,6 +12229,7 @@ html .column.drag-over * {
   text-align: center;
   flex: 1;
   min-height: 0;
+  overflow: hidden;
 }
 
 .planning-intro {
@@ -12758,7 +12759,6 @@ html .column.drag-over * {
   flex-direction: column;
   align-items: center;
   justify-content: center;
-  min-height: 300px;
   gap: var(--space-lg);
   padding: var(--space-xl);
   color: var(--text-muted);