feat(web): make google cast opt in (#18514)

* add setting switch

this isnt bound to anything yet

* make google casting opt-in

* doc updates

* lint docs

* remove unneeded translation items

* update mobile openai defs

* fix failing test

we need to mock user prefs since CastButton uses it

web/src/lib/components/user-settings-page/feature-settings.svelte

@@ -34,6 +34,9 @@
   let tagsEnabled = $state($preferences?.tags?.enabled ?? false);
   let tagsSidebar = $state($preferences?.tags?.sidebarWeb ?? false);
 
+  // Cast
+  let gCastEnabled = $state($preferences?.cast?.gCastEnabled ?? false);
+
   const handleSave = async () => {
     try {
       const data = await updateMyPreferences({
@@ -44,6 +47,7 @@
           ratings: { enabled: ratingsEnabled },
           sharedLinks: { enabled: sharedLinksEnabled, sidebarWeb: sharedLinkSidebar },
           tags: { enabled: tagsEnabled, sidebarWeb: tagsSidebar },
+          cast: { gCastEnabled },
         },
       });
 
@@ -138,6 +142,16 @@
           {/if}
         </SettingAccordion>
 
+        <SettingAccordion key="cast" title={$t('cast')} subtitle={$t('cast_description')}>
+          <div class="ms-4 mt-6">
+            <SettingSwitch
+              title={$t('gcast_enabled')}
+              subtitle={$t('gcast_enabled_description')}
+              bind:checked={gCastEnabled}
+            />
+          </div>
+        </SettingAccordion>
+
         <div class="flex justify-end">
           <Button shape="round" type="submit" size="small" onclick={() => handleSave()}>{$t('save')}</Button>
         </div>