Implement error handling in app.py, update deployment instructions in README_DASHBOARD.md, and modify deploy.sh for rsync-based deployment. Adjust base.html to safely access session variables.

templates/base.html

@@ -22,7 +22,7 @@
       <a href="{{ url_for('table_view', name='sessions') }}">Sessions</a>
       <a href="{{ url_for('table_view', name='auth_logs') }}">Auth logs</a>
       <a href="{{ url_for('table_view', name='api_tokens') }}">API tokens</a>
-      <span class="user">{{ session.admin_username }}</span>
+      <span class="user">{{ session.get('admin_username', '') }}</span>
       <a href="{{ url_for('logout') }}" class="logout">Log out</a>
     </nav>
     {% endif %}