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>
 

Web/View/StaticPages/Landing.hs

@@ -115,9 +115,9 @@ instance View LandingView where
         </div>
     |]
       where
-        chainLink label color = [hsx|
+        chainLink (label :: Text) (color :: Text) = [hsx|
             <span class={"inline-block px-2 py-1 rounded text-xs bg-" <> color <> "-100 text-" <> color <> "-800 font-mono"}>
-                {label :: Text}
+                {label}
             </span>
         |]
         arrow = [hsx|<span class="text-gray-400">→</span>|]

Web/View/StaticPages/Tutorial.hs

@@ -25,7 +25,7 @@ instance View TutorialView where
                 </p>
                 <div class="bg-gray-900 rounded-lg p-4 text-sm font-mono text-green-400">
                     <div class="text-gray-400 mb-1">-- Every rendered widget wraps its HSX in widgetEnvelope</div>
-                    widgetEnvelope widgetId viewContext [hsx|...|]
+                    {"widgetEnvelope widgetId viewContext [hsx|...|]" :: Text}
                 </div>
                 <p class="text-sm text-gray-500 mt-2">
                     The envelope injects <code>data-widget-id</code> and <code>data-view-context</code> attributes,