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/routes/pages.py

@@ -5,12 +5,14 @@ from __future__ import annotations
 from fastapi import APIRouter, Request
 from fastapi.templating import Jinja2Templates
 
+from backend.database import is_available
+
 router = APIRouter()
 templates = Jinja2Templates(directory="backend/templates")
 
 
 def _ctx(request: Request, page: str, **extra) -> dict:
-    return {"request": request, "active_page": page, **extra}
+    return {"request": request, "active_page": page, "ch_available": is_available(), **extra}
 
 
 @router.get("/")