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/test_helper.rb

@@ -17,6 +17,18 @@ module ActiveSupport
     fixtures :all
 
     # Add more helper methods to be used by all tests here...
+    
+    # Helper to create users with completed onboarding by default for tests
+    def create_test_user(attributes = {})
+      User.create!({
+        email: "test#{rand(10000)}@example.com",
+        password: "password123",
+        password_confirmation: "password123",
+        first_name: "Test",
+        last_name: "User",
+        onboarding_completed: true
+      }.merge(attributes))
+    end
   end
 end