Bulk Approve Agent Drafts

Approve + send many of an agent's PENDING drafts. Sending must run on the worker (Resend's 1 req/s, exactly-once), so this ENQUEUES the sends and returns 202 with the count that will be processed. draft_ids = explicit selection; only_safe=true (with no ids) sends every 'safe'-tier pending draft and never a flagged/uncertain one, scoped to filters (same semantics as the /drafts/page recipient filters) when provided, so a filtered review queue's 'Approve N safe' sends exactly the filtered set, all pages.