feat: Implement comprehensive onboarding system for new users

Add complete user onboarding flow that redirects new users to complete their
profile before accessing the application:

- Add onboarding_completed boolean field to users with migration
- Create OnboardingController with form validation and completion logic
- Design professional onboarding UI with progressive disclosure for company info
- Implement Stimulus controller for toggling company information section
- Add application-wide redirect middleware for incomplete users
- Create comprehensive test suite for all onboarding functionality
- Update test fixtures and helpers to support onboarding in existing tests

The onboarding collects required first/last name and optional company information.
Users are redirected to onboarding after login until profile is completed.
Features smooth animations, full-width form button, and clean UX design.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

test/controllers/onboarding_controller_test.rb

@@ -0,0 +1,104 @@
+require "test_helper"
+
+class OnboardingControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @user_without_onboarding = users(:one)
+    @user_without_onboarding.update!(onboarding_completed: false)
+    
+    @user_with_onboarding = users(:two)
+    @user_with_onboarding.update!(onboarding_completed: true, first_name: "John", last_name: "Doe")
+  end
+
+  test "should redirect to onboarding when user not signed in" do
+    get onboarding_path
+    assert_redirected_to new_user_session_path
+  end
+
+  test "should show onboarding page for incomplete user" do
+    sign_in @user_without_onboarding
+    get onboarding_path
+    assert_response :success
+    assert_select "h1", "Bienvenue sur AperoNight !"
+    assert_select "form"
+  end
+
+  test "should redirect completed user to dashboard" do
+    sign_in @user_with_onboarding
+    get onboarding_path
+    assert_redirected_to dashboard_path
+  end
+
+  test "should complete onboarding with valid data" do
+    sign_in @user_without_onboarding
+    
+    assert_not @user_without_onboarding.onboarding_completed?
+    
+    post complete_onboarding_path, params: {
+      user: {
+        first_name: "Jane",
+        last_name: "Smith",
+        company_name: "Test Company"
+      }
+    }
+    
+    assert_redirected_to dashboard_path
+    follow_redirect!
+    assert_select ".notification", /Bienvenue sur AperoNight/
+    
+    @user_without_onboarding.reload
+    assert @user_without_onboarding.onboarding_completed?
+    assert_equal "Jane", @user_without_onboarding.first_name
+    assert_equal "Smith", @user_without_onboarding.last_name
+    assert_equal "Test Company", @user_without_onboarding.company_name
+  end
+
+  test "should complete onboarding without optional company name" do
+    sign_in @user_without_onboarding
+    
+    post complete_onboarding_path, params: {
+      user: {
+        first_name: "Jane",
+        last_name: "Smith",
+        company_name: ""
+      }
+    }
+    
+    assert_redirected_to dashboard_path
+    @user_without_onboarding.reload
+    assert @user_without_onboarding.onboarding_completed?
+  end
+
+  test "should not complete onboarding without required fields" do
+    sign_in @user_without_onboarding
+    
+    post complete_onboarding_path, params: {
+      user: {
+        first_name: "",
+        last_name: "Smith"
+      }
+    }
+    
+    assert_response :success
+    assert_select ".notification", /Veuillez remplir tous les champs requis/
+    
+    @user_without_onboarding.reload
+    assert_not @user_without_onboarding.onboarding_completed?
+  end
+
+  test "should not complete onboarding without last name" do
+    sign_in @user_without_onboarding
+    
+    post complete_onboarding_path, params: {
+      user: {
+        first_name: "Jane",
+        last_name: ""
+      }
+    }
+    
+    assert_response :success
+    assert_select ".notification", /Veuillez remplir tous les champs requis/
+    
+    @user_without_onboarding.reload
+    assert_not @user_without_onboarding.onboarding_completed?
+  end
+end