feat(i18n + export + guide): locale-aware scenarios/debrief; CSV export; how-to-use page

Backend:
- SCENARIOS localized (th/en): scenario preamble + persona tone adaptation follow the
  trainee's locale; start accepts {locale} and stores it on the session; send/auto-finish
  use it so debrief text (why/coaching/turning points) is in the active language.
- /api/analytics/export returns per-trainee finished-session CSV (admin).

Frontend:
- Scenario picker labels localize by i18n.locale.
- New /guide page (non-IT how-to), linked from Training.
- Analytics: date-filter bar uses line icon + 'Download CSV' button (fetch w/ auth).
Rebuilt dist.

frontend/dist/assets/Training-BYBkfggr.css

@@ -0,0 +1 @@
+.grid[data-v-e39df241]{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:16px}.train-card[data-v-e39df241]{display:flex;flex-direction:column;height:100%}.badge.ready[data-v-e39df241]{background:#dcfce7;color:#166534}.badge.draft[data-v-e39df241]{background:#fef9c3;color:#854d0e}button.soft[data-v-e39df241]{background:#f1f3f9;border-color:transparent}.badge.facebook[data-v-e39df241]{background:#e0f2fe;color:#0369a1}.badge.line[data-v-e39df241]{background:#dcfce7;color:#15803d}