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>

app/controllers/application_controller.rb

@@ -5,6 +5,9 @@ class ApplicationController < ActionController::Base
   # Ensures that all non-GET requests include a valid authenticity token
   protect_from_forgery with: :exception
 
+  # Redirect authenticated users to onboarding if not completed
+  before_action :require_onboarding_completion
+
   # Restrict access to modern browsers only
   # Requires browsers to support modern web standards:
   # - WebP images for better compression
@@ -14,4 +17,29 @@ class ApplicationController < ActionController::Base
   # - CSS nesting and :has() pseudo-class
   # allow_browser versions: :modern
   # allow_browser versions: { safari: 16.4, firefox: 121, ie: false }
+
+  private
+
+  def require_onboarding_completion
+    # Skip onboarding check for these paths
+    return if skip_onboarding_check?
+
+    # Only apply to signed-in users
+    if user_signed_in? && current_user.needs_onboarding?
+      redirect_to onboarding_path unless request.path == onboarding_path
+    end
+  end
+
+  def skip_onboarding_check?
+    # Skip for devise controllers (login, signup, password reset, etc.)
+    devise_controller? ||
+    # Skip for onboarding controller itself
+    controller_name == "onboarding" ||
+    # Skip for API endpoints
+    controller_name.start_with?("api/") ||
+    # Skip for health checks
+    controller_name == "rails/health" ||
+    # Skip for home page (when not signed in)
+    (controller_name == "pages" && action_name == "home")
+  end
 end