feat(P6/T04): WidgetAdapterSpecsController, registry, widget adapter integration

CRUD for WidgetAdapterSpec (index, show, new/create, edit/update — status+notes only
after creation). Widget new/edit forms expose optional adapter_spec_id select.
Widget show page renders adapter badge with link to spec. Widgets controller
fetches adapter spec for show action.

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

Web/View/Widgets/New.hs

@@ -6,20 +6,21 @@ import IHP.Prelude
 import IHP.ViewPrelude
 
 data NewView = NewView
-    { widget :: !Widget
-    , hubs   :: ![Hub]
+    { widget       :: !Widget
+    , hubs         :: ![Hub]
+    , adapterSpecs :: ![WidgetAdapterSpec]
     }
 
 instance View NewView where
     html NewView { .. } = [hsx|
         <div class="max-w-lg">
             <h1 class="text-2xl font-semibold mb-6">Register Widget</h1>
-            {renderForm widget hubs}
+            {renderForm widget hubs adapterSpecs}
         </div>
     |]
 
-renderForm :: Widget -> [Hub] -> Html
-renderForm widget hubs = formFor widget [hsx|
+renderForm :: Widget -> [Hub] -> [WidgetAdapterSpec] -> Html
+renderForm widget hubs adapterSpecs = formFor widget [hsx|
     {textField #name}
     {selectField #widgetType widgetTypeOptions}
     {selectField #hubId (hubOptions hubs)}
@@ -27,6 +28,15 @@ renderForm widget hubs = formFor widget [hsx|
     {textField #viewContext}
     {selectField #policyScope policyScopeOptions}
     {selectField #status statusOptions}
+    <div>
+        <label class="ihp-form-label">Adapter Spec (optional — leave blank for native IHP widget)</label>
+        <select name="adapterSpecId" class="ihp-form-field">
+            <option value="">— Native IHP widget —</option>
+            {forEach adapterSpecs (\s -> [hsx|
+                <option value={tshow s.id}>{s.name} ({s.framework} v{s.version})</option>
+            |])}
+        </select>
+    </div>
     {submitButton}
 |]