fix(web): stop exporting formatDuration from runs settings page

Next.js App Router rejects non-page exports from page modules; duration
formatting stays a local helper.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/web/app/(app)/[workspaceSlug]/settings/runs/page.tsx

@@ -66,7 +66,7 @@ function formatTimestamp(when: Date | string): string {
  * for in-flight runs (no `finishedAt`). Below a minute we show seconds
  * with a single decimal so quick MCP calls don't all look like "0s".
  */
-export function formatDuration(
+function formatDuration(
   startedAt: Date | string,
   finishedAt: Date | string | null,
 ): string {