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/javascript/controllers/toggle_section_controller.js

@@ -0,0 +1,25 @@
+import { Controller } from "@hotwired/stimulus"
+
+// Connects to data-controller="toggle-section"
+export default class extends Controller {
+  static targets = ["section", "icon"]
+  
+  connect() {
+    // Ensure the section starts hidden
+    this.sectionTarget.classList.add("hidden")
+  }
+  
+  toggle() {
+    const isHidden = this.sectionTarget.classList.contains("hidden")
+    
+    if (isHidden) {
+      // Show the section
+      this.sectionTarget.classList.remove("hidden")
+      this.iconTarget.classList.add("rotate-180")
+    } else {
+      // Hide the section
+      this.sectionTarget.classList.add("hidden")
+      this.iconTarget.classList.remove("rotate-180")
+    }
+  }
+}