Fix test dashboard: return SX wire format for SX-Request on index route

Filter card links (/?filter=failed) were blanking the page because the
index route always returned full HTML, even for SX-Request. Now returns
sx_response() partial like test_detail already does.

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

test/bp/dashboard/routes.py

@@ -12,18 +12,29 @@ def register(url_prefix: str = "/") -> Blueprint:
     @bp.get("/")
     async def index():
         """Full page dashboard with last results."""
-        from shared.sx.page import get_template_context
         from shared.browser.app.csrf import generate_csrf_token
-        from sxc.pages.renders import render_dashboard_page_sx
+        from sxc.pages.renders import render_dashboard_page_sx, render_results_partial_sx
         import runner
 
-        ctx = await get_template_context()
         result = runner.get_results()
         running = runner.is_running()
         csrf = generate_csrf_token()
         active_filter = request.args.get("filter")
         active_service = request.args.get("service")
 
+        is_sx = bool(request.headers.get("SX-Request") or request.headers.get("HX-Request"))
+
+        if is_sx:
+            from shared.sx.helpers import sx_response
+            html = await render_results_partial_sx(
+                result, running, csrf,
+                active_filter=active_filter,
+                active_service=active_service,
+            )
+            return sx_response(html)
+
+        from shared.sx.page import get_template_context
+        ctx = await get_template_context()
         html = await render_dashboard_page_sx(
             ctx, result, running, csrf,
             active_filter=active_filter,