Fix test dashboard SX swap targets for partial responses

Filter cards: target #test-results (the actual response container)
instead of sx-select #main-panel (not present in partial response).
Back link: use innerHTML swap into #main-panel (no sx-select needed).
Results route: use sx_response() for correct content-type.

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

test/sx/dashboard.sx

@@ -20,8 +20,7 @@
 (defcomp ~test-filter-card (&key href label count colour-border colour-bg colour-text active)
   (a :href href
      :sx-get href
-     :sx-target "#main-panel"
-     :sx-select "#main-panel"
+     :sx-target "#test-results"
      :sx-swap "outerHTML"
      :sx-push-url "true"
      :class (str "block rounded border p-3 text-center transition-colors no-underline hover:opacity-80 "
@@ -126,8 +125,7 @@
       (a :href "/"
          :sx-get "/"
          :sx-target "#main-panel"
-         :sx-select "#main-panel"
-         :sx-swap "outerHTML"
+         :sx-swap "innerHTML"
          :sx-push-url "true"
          :class "text-sky-600 hover:text-sky-800 text-sm"
         "← Back to results")