feat(e2e): add distributed E2E test framework with parametric traffic generation

Add run-e2e-test.sh with CLI parameters (--hits, --http-ratio, --dns, --tls,
--src-ips, --keep-analysis, --up) for configurable traffic generation. Traffic
runs from VM endpoints with multiple source IPs (alias IPs on eth0) to produce
distinct sessions for the ML pipeline. Fix curl TLS flags (--tlsv1.2 instead
of --tls-v1-2), skip redundant local verification in distributed mode, and
fix dashboard is_available() cache that never retried after ClickHouse recovery.

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

services/dashboard/backend/templates/base.html

@@ -219,6 +219,12 @@
                 {% block header_actions %}{% endblock %}
             </div>
         </header>
+        {% if not ch_available %}
+        <div id="ch-banner" class="bg-amber-900/60 border-b border-amber-600 px-4 py-2 text-amber-200 text-sm flex items-center gap-2">
+            <svg class="w-4 h-4 shrink-0" fill="none" stroke="currentColor" stroke-width="2" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" d="M12 9v3.75m-9.303 3.376c-.866 1.5.217 3.374 1.948 3.374h14.71c1.73 0 2.813-1.874 1.948-3.374L13.949 3.378c-.866-1.5-3.032-1.5-3.898 0L2.697 16.126zM12 15.75h.008v.008H12v-.008z"/></svg>
+            <span><strong>ClickHouse indisponible</strong> — Les données ne peuvent pas être chargées. Vérifiez la connexion au serveur.</span>
+        </div>
+        {% endif %}
         <main class="px-3 py-4 lg:px-5 lg:py-5 xl:px-6">
             {% block content %}{% endblock %}
         </main>