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/SlidesExport.jsx

@@ -1,4 +1,4 @@
-// Export → Slides: a printable slide deck for a session or the whole study (Save as PDF in the print dialog).
+// Finish → Slides: a printable slide deck for a session or the whole study (Save as PDF in the print dialog).
 import { useState } from 'react';
 import { sessionsFor } from '../utils/handout.js';
 import { printSlides } from '../utils/slides.js';