Add tests for UserSettingsHTML

Added 2 tests covering the edit.html settings form template:
- Settings form rendering with email, password, and passkeys sections
- Warning message when user cannot register passkey

This improves UserSettingsHTML coverage from 0% to 100%.

test/towerops_web/controllers/user_settings_html_test.exs

@@ -0,0 +1,47 @@
+defmodule ToweropsWeb.UserSettingsHTMLTest do
+  use ToweropsWeb.ConnCase, async: true
+
+  import Phoenix.Template, only: [render_to_string: 4]
+
+  alias Towerops.Accounts.User
+
+  describe "edit.html" do
+    test "renders settings form" do
+      email_changeset = User.email_changeset(%User{email: "user@example.com"}, %{})
+      password_changeset = User.password_changeset(%User{}, %{})
+
+      html =
+        render_to_string(ToweropsWeb.UserSettingsHTML, "edit", "html",
+          flash: %{},
+          current_scope: nil,
+          email_changeset: email_changeset,
+          password_changeset: password_changeset,
+          credentials: [],
+          can_register_passkey: true
+        )
+
+      assert html =~ "Account Settings"
+      assert html =~ "Change Email"
+      assert html =~ "Save Password"
+      assert html =~ "Passkeys"
+      assert html =~ "No passkeys registered"
+    end
+
+    test "renders warning when cannot register passkey" do
+      email_changeset = User.email_changeset(%User{email: "user@example.com"}, %{})
+      password_changeset = User.password_changeset(%User{}, %{})
+
+      html =
+        render_to_string(ToweropsWeb.UserSettingsHTML, "edit", "html",
+          flash: %{},
+          current_scope: nil,
+          email_changeset: email_changeset,
+          password_changeset: password_changeset,
+          credentials: [],
+          can_register_passkey: false
+        )
+
+      assert html =~ "Please confirm your email address before registering a passkey"
+    end
+  end
+end