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/StaticPages/ExtensionGuide.hs

@@ -85,10 +85,10 @@ instance View ExtensionGuideView where
                 </p>
                 <div class="bg-gray-900 rounded-lg p-4 text-sm font-mono text-green-400">
                     POST /api/v2/widgets<br/>
-                    <span class="text-gray-400">{"{"} "name": "PR Review Widget",<br/>
+                    <span class="text-gray-400">&#123; "name": "PR Review Widget",<br/>
                     &nbsp;&nbsp;"widgetType": "dev.code-review",<br/>
                     &nbsp;&nbsp;"hubId": "...",<br/>
-                    &nbsp;&nbsp;"viewContext": "pull-request-sidebar" {"}"}</span>
+                    &nbsp;&nbsp;"viewContext": "pull-request-sidebar" &#125;</span>
                 </div>
             </section>