FIX: correctly handles mobile and default (#23152)

This commit ensures we have correct icon and title on mobile for the chat header icon.

It also fixes a bug where the site setting was not correctly used when the user has not yet set the user option.

Both cases are now correctly tested.

plugins/chat/test/javascripts/components/chat-header-icon-test.js

@@ -41,4 +41,17 @@ module("Discourse Chat | Component | chat-header-icon", function (hooks) {
 
     assert.dom(".d-icon-random").exists();
   });
+
+  test("mobile", async function (assert) {
+    this.site.mobileView = true;
+
+    await render(hbs`<Chat::Header::Icon />`);
+
+    assert
+      .dom(".icon.btn-flat")
+      .hasAttribute("title", I18n.t("chat.title_capitalized"))
+      .hasAttribute("href", "/chat");
+
+    assert.dom(".d-icon-d-chat").exists();
+  });
 });