Operator marker: "I sent this mission by hand."

The gap this closes (the Cosankov case, 2026-05-19): when a mission's outreach_channel is 'manual' — or whenever the operator sends the DM / public reply themselves via the platform UI instead of letting the sidecar/daemon send it — nothing tells the brain the send happened. The mission sits in 'approved'/'draft_needed' forever, no prospect is born, no message_sent interaction is logged, and a later get_message_prompt follow-up draft is blind to what we already said.

This is the operator-side equivalent of a successful /actions/ack:

1. flips the mission to 'sent',
2. fires the same positive 'replied' RL nudge as /actions/approve — a manual send is an endorsement, and under the temperature-gated DM model (see project_signalpipe_v4_plan.md §3.6) manual / public first-touch is the COMMON path, so its RL signal must not be lost,
3. records the outbound message (prospect upsert at temperature=10 / mode=nurture + message_sent interaction + last_signal).

All three helpers are idempotent, so the operator calling /actions/approve first and /actions/mark_sent second does NOT double-fire RL or duplicate the interaction row.

Body: { "id": "<mission_id>" }