fix: cap new issue dialog height so long descriptions don't hide controls

The description area in the non-expanded NewIssueDialog could grow
unboundedly, pushing the property chips and footer off-screen. Now
the dialog has max-h-[calc(100vh-6rem)] in both modes, and the
description wrapper scrolls when content overflows.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/NewIssueDialog.tsx

@@ -237,9 +237,9 @@ export function NewIssueDialog() {
       <DialogContent
         showCloseButton={false}
         className={cn(
-          "p-0 gap-0 flex flex-col",
+          "p-0 gap-0 flex flex-col max-h-[calc(100vh-6rem)]",
           expanded
-            ? "sm:max-w-2xl h-[calc(100vh-6rem)] max-h-[calc(100vh-6rem)]"
+            ? "sm:max-w-2xl h-[calc(100vh-6rem)]"
             : "sm:max-w-lg"
         )}
         onKeyDown={handleKeyDown}
@@ -293,7 +293,7 @@ export function NewIssueDialog() {
         </div>
 
         {/* Description */}
-        <div className={cn("px-4 pb-2", expanded ? "flex-1 min-h-0" : "")}>
+        <div className={cn("px-4 pb-2 overflow-y-auto min-h-0", expanded ? "flex-1" : "")}>
           <MarkdownEditor
             ref={descriptionEditorRef}
             value={description}