Add Craft Commerce order event support (placed + paid)

[chasegiunta]

Summary

Adds Craft Commerce order notifications to Notifier with two new trigger events:

• after-complete-order (order placed/completed)
• after-order-paid (order fully paid)

What changed

• Added commerce-orders event type and events in Options
• Registered Commerce order listeners in Events service, behind class_exists(Order::class) so non-Commerce installs remain safe
• Added new event handler class CommerceOrderEvents
• Added CP UI select for Commerce order events
• Updated Dispatch::filterByEventType() to accept commerce-orders

Notes

• This keeps Commerce support optional and backward-compatible
• No new recipient/message behavior changes, only new event sources