Rename the Export stage to Finish

It now holds files, sharing, handouts, slides, importing notes, schedule,
co-teachers and earlier versions, not just exports.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/components/VersionHistory.jsx

@@ -1,4 +1,4 @@
-// Export → Earlier versions: the copies the server kept of this study as you worked. Look at what is different
+// Finish → Earlier versions: the copies the server kept of this study as you worked. Look at what is different
 // from now, and put one back. The version you replace is kept, so putting one back can be undone too.
 import { useCallback, useEffect, useState } from 'react';
 import { getStudyVersion, listStudyVersions } from '../syncService.js';