feat(frontend): T46 configure HTMX and CSRF protection

- Add CSRFMiddleware for form protection
- Implement token generation and validation
- Add CSRF meta tag to base.html
- Create tests for CSRF protection

Tests: 13 passing

templates/base.html

@@ -4,9 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <meta name="description" content="OpenRouter API Key Monitor - Monitor and manage your OpenRouter API keys">
-    {% if csrf_token %}
-    <meta name="csrf-token" content="{{ csrf_token }}">
-    {% endif %}
+    <meta name="csrf-token" content="{{ request.state.csrf_token or '' }}">
     <title>{% block title %}OpenRouter Monitor{% endblock %}</title>
     
     <!-- Pico.css for styling -->