feature/account-self-delete-and-subscription-mgmt
master
Add account_deleted, subscription_started, and subscription_updated event types. Soft-delete, Checkout/Backer assign, and Stripe portal lifecycle webhooks write audit rows visible on the user admin.
Soft-delete DELETE /api/user/ for authenticated users (hide conversations, blacklist tokens, block staff self-delete). Sync Stripe portal cancel/change via subscription.updated/deleted webhooks and expose cancel_at_period_end for Account UI (chat_web_app#75 companion).