Add dual user classes: admin + tech users with PIN login

- Add tech user management (JSON-backed CRUD with PIN auth)
- Dual login: tabbed Tech Login (username+PIN) / Admin Login (NC credentials)
- Admin panel: tappable user list with detail modal (enable/disable, reset PIN, reset NC password, delete)
- Auto-provision Nextcloud accounts for tech users
- Admin guard: tech users redirected away from admin panel
- New data volume for persistent tech_users.json storage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/routes/views.py

@@ -82,7 +82,7 @@ def admin():
     if 'username' not in session:
         return redirect(url_for('views.login_page'))
     if not session.get('is_admin', False):
-        return "Access denied: Admin privileges required", 403
+        return redirect(url_for('views.capture'))
     return render_template(
         'admin.html',
         username=session['username'],