fix(tasks): block Cancel and Escape from closing generate dialog mid-request

AlertDialogCancel and Escape both closed the confirmation dialog via
Radix's default onOpenChange(false) while the generate-and-assign
fetch was still in flight, leaving an orphaned request that could
resolve after the user believed they'd cancelled and could leave
`generating` stuck true. Disable Cancel and suppress onEscapeKeyDown
while `generating` is true so the dialog can only close intentionally
once the request settles.

ondeck/src/app/(dashboard)/tasks/assign/page-client.tsx

@@ -329,7 +329,11 @@ export function BulkAssignClient({ users, clients, designations }: BulkAssignCli
       </Card>
 
       <AlertDialog open={!!preview} onOpenChange={(open) => { if (!open) setPreview(null) }}>
-        <AlertDialogContent>
+        <AlertDialogContent
+          onEscapeKeyDown={(event) => {
+            if (generating) event.preventDefault()
+          }}
+        >
           <AlertDialogHeader>
             <AlertDialogTitle>
               Generate {preview?.totalEstimatedTasks} task{preview && preview.totalEstimatedTasks !== 1 ? 's' : ''}?
@@ -358,7 +362,7 @@ export function BulkAssignClient({ users, clients, designations }: BulkAssignCli
             </Table>
           </div>
           <AlertDialogFooter>
-            <AlertDialogCancel>Cancel</AlertDialogCancel>
+            <AlertDialogCancel disabled={generating}>Cancel</AlertDialogCancel>
             <AlertDialogAction onClick={handleConfirmGenerate} disabled={generating}>
               {generating ? 'Generating...' : 'Confirm'}
             </AlertDialogAction>