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.

backend/app/api/analytics_routes.py

@@ -111,3 +111,63 @@ def analytics():
         "trainee_count": len(users),
         "hardest_personas": hardest,
     })
+
+
+@analytics_bp.get("/export")
+@require_auth
+@require_roles("admin")
+def export_csv():
+    """Export per-trainee finished session results as CSV (for HR/offline review)."""
+    import csv
+    import io
+
+    from flask import Response, current_app
+
+    s = _stores()
+    users = {}
+    try:
+        user_store = current_app.extensions.get("user_store")
+        if user_store and hasattr(user_store, "list_users"):
+            for rec in user_store.list_users():
+                users[rec.get("id") or rec.get("username")] = rec.get("username") or rec.get("id")
+    except Exception:
+        pass
+
+    sessions = []
+    try:
+        grp_store = s["groups"]
+        sess_store = s["sessions"]
+        if hasattr(grp_store, "groups"):
+            group_ids = [g.get("id") for g in grp_store.groups.all()]
+        elif hasattr(grp_store, "all"):
+            group_ids = [g.get("id") for g in grp_store.all()]
+        else:
+            group_ids = []
+        for gid in group_ids:
+            try:
+                ss = sess_store.sessions.where(
+                    lambda r, _gid=gid: r.get("group_id") == _gid and r.get("outcome")
+                )
+                sessions.extend(ss)
+            except Exception:
+                pass
+    except Exception:
+        pass
+
+    buf = io.StringIO()
+    w = csv.writer(buf)
+    w.writerow(["username", "persona", "scenario", "outcome", "score", "created_at"])
+    for sess in sessions:
+        w.writerow([
+            users.get(sess.get("user_id"), sess.get("user_id", "")),
+            sess.get("persona_name", ""),
+            sess.get("scenario", ""),
+            sess.get("outcome", ""),
+            (sess.get("debrief") or {}).get("score", ""),
+            sess.get("created_at", ""),
+        ])
+    return Response(
+        buf.getvalue(),
+        mimetype="text/csv",
+        headers={"Content-Disposition": "attachment; filename=sales-trainer-results.csv"},
+    )