fix(WP-0017/E3): Layer 3 error fixes — controllers and views

Fix compilation errors across 6 controllers and 29 views: import cleanup,
ResponseException pattern for API auth, type fixes, unused import removal.

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

Web/View/PatternPerformance/Index.hs

@@ -58,7 +58,6 @@ instance View IndexView where
 renderRecomputeButton :: Hub -> Html
 renderRecomputeButton h = [hsx|
     <form method="POST" action={ComputePatternPerformanceAction (h.id)} class="inline">
-        {csrfTokenTag}
         <button type="submit"
             class="px-3 py-1.5 text-sm bg-indigo-600 text-white rounded hover:bg-indigo-700">
             Recompute for {h.name}