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>

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_08_23_171354) do
+ActiveRecord::Schema[8.0].define(version: 2025_09_08_092220) do
   create_table "events", charset: "utf8mb4", collation: "utf8mb4_uca1400_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "slug", null: false
@@ -94,6 +94,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_08_23_171354) do
     t.string "stripe_customer_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.boolean "onboarding_completed", default: false, null: false
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
   end