Subscriptions now declare a `verb` (create | delete | bulk-create).
POST /:did/webhooks defaults to inserting both create and delete rows
when no verb is given, preserving existing all-events behavior. Update
events fold into the create verb. The new bulk-create verb debounces
creates per DID over 400 ms and delivers a `records` array.
Migration adds the verb column with default 'create' and clones every
existing row for the delete verb so legacy subscriptions keep firing
on both events.
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