Move AI enable endpoint to user scope

Replace /api/v1/auth/enable_ai with /api/v1/user/enable_ai by moving the action into Api::V1::UsersController, updating Flutter client calls, tests, and OpenAPI docs.

test/controllers/api/v1/users_controller_test.rb

@@ -0,0 +1,40 @@
+require "test_helper"
+
+class Api::V1::UsersControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @user = users(:family_admin)
+    @user.update!(ai_enabled: false)
+
+    @shared_app = Doorkeeper::Application.find_or_create_by!(name: "Sure Mobile") do |app|
+      app.redirect_uri = "sureapp://oauth/callback"
+      app.scopes = "read_write"
+      app.confidential = false
+    end
+
+    @token = Doorkeeper::AccessToken.create!(
+      application: @shared_app,
+      resource_owner_id: @user.id,
+      scopes: "read_write"
+    )
+  end
+
+  test "should enable ai for authenticated user" do
+    patch "/api/v1/user/enable_ai", headers: {
+      "Authorization" => "Bearer #{@token.token}",
+      "Content-Type" => "application/json"
+    }
+
+    assert_response :success
+
+    response_data = JSON.parse(response.body)
+    assert_equal true, response_data.dig("user", "ai_enabled")
+    assert_equal @user.ui_layout, response_data.dig("user", "ui_layout")
+    assert @user.reload.ai_enabled?
+  end
+
+  test "should require authentication when enabling ai" do
+    patch "/api/v1/user/enable_ai", headers: { "Content-Type" => "application/json" }
+
+    assert_response :unauthorized
+  end
+end