fix render lifecycle race: await ink unmount before resolving

renderTasks and renderSingleTask resolved their promises via
onComplete={resolve}, which fires inside the React tree before
ink unmounts. This caused the caller to write to stdout while
ink was still tearing down, resulting in loading bars staying
visible and last lines of output being cut off.

Changed both functions to await render() (which awaits
waitUntilExit()) before returning, matching the pattern the
prompt functions already use.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ryancbahan

packages/cli-kit/src/public/node/ui.tsx

@@ -486,7 +486,7 @@ interface RenderTasksOptions {
 export async function renderTasks<TContext>(
   tasks: Task<TContext>[],
   {renderOptions, noProgressBar}: RenderTasksOptions = {},
-) {
+): Promise<TContext> {
   let taskResult: TContext
   await render(
     <Tasks