Migrate admin_v2 Namespace to admin

[americac]

!!! Blocked By: #945 !!!

Description:
Rename admin_v2 namespace to admin and move routes from /admin-new to /admin. Keep Administrate installed as safety net until Ticket 24.

Tasks:

• Rename Admin::V2::* controllers to Admin::*
  • Move app/controllers/admin/v2/ to app/controllers/admin/
  • Update all controller class names (remove ::V2)
• Rename view directories
  • Move app/views/admin_v2/ to app/views/admin/
• Rename layout
  • Rename app/views/layouts/admin_v2.html.erb to admin.html.erb
• Rename components/helpers
  • Move app/components/admin/v2/ to app/components/admin/
  • Move app/helpers/admin/v2_helper.rb to app/helpers/admin_helper.rb
  • Move app/form_builders/admin/v2/ to app/form_builders/admin/
• Update routes configuration
  • Comment out namespace :admin do (Administrate block) - don't delete yet
  • Rename namespace :admin_v2, path: 'admin-new' do to namespace :admin do
  • Remove path override (now uses /admin)
  • Set admin root to admin/classrooms#index
• Update all internal references to remove V2 namespace
• Do NOT remove Administrate gem yet (safety net for rollback)

Acceptance Criteria:

• All controllers renamed from Admin::V2::* to Admin::*
• All views moved from admin_v2/ to admin/
• All components/helpers moved and renamed
• Routes updated: in-house admin now at /admin/*
• Admin root accessible at /admin (not /admin-new)
• No references to Admin::V2 or admin_v2 remain
• All admin pages load correctly at /admin/*
• All tests pass
• No broken links or errors in admin interface
• Administrate gem still installed (can rollback if needed)

Files to Rename/Move:

• app/controllers/admin/v2/ → app/controllers/admin/
• app/views/admin_v2/ → app/views/admin/
• app/views/layouts/admin_v2.html.erb → app/views/layouts/admin.html.erb
• app/components/admin/v2/ → app/components/admin/
• app/helpers/admin/v2_helper.rb → app/helpers/admin_helper.rb
• app/form_builders/admin/v2/ → app/form_builders/admin/

Files to Update:

• config/routes.rb (comment out Administrate routes, activate new admin routes)