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/models/user_test.rb

@@ -63,4 +63,33 @@ class UserTest < ActiveSupport::TestCase
     refute user.valid?, "User with last_name longer than 12 chars should be invalid"
     assert_not_nil user.errors[:last_name], "No validation error for too long last_name"
   end
+
+  # Test onboarding functionality
+  test "new users should need onboarding by default" do
+    user = User.new(email: "test@example.com", password: "password123")
+    assert user.needs_onboarding?, "New user should need onboarding"
+    assert_not user.onboarding_completed?, "New user should not have completed onboarding"
+  end
+
+  test "should complete onboarding" do
+    user = users(:one)
+    user.update!(onboarding_completed: false)
+    
+    assert user.needs_onboarding?, "User should need onboarding initially"
+    
+    user.complete_onboarding!
+    
+    assert_not user.needs_onboarding?, "User should not need onboarding after completion"
+    assert user.onboarding_completed?, "User should have completed onboarding"
+  end
+
+  test "needs_onboarding? should return correct value" do
+    user = users(:one)
+    
+    user.update!(onboarding_completed: false)
+    assert user.needs_onboarding?, "User with false onboarding_completed should need onboarding"
+    
+    user.update!(onboarding_completed: true)
+    assert_not user.needs_onboarding?, "User with true onboarding_completed should not need onboarding"
+  end
 end