Pre-flight readiness probe used by the cohort Groups tab to gate the Start Matching button. Mirrors the same checks that MatchingPayloadBuilder.build() would throw on, so admins see the blockers before clicking instead of via a 4xx toast after.

Checks (in priority order):

• Cohort has intake_form_id configured.
• At least one active, non-deleted participant has non-empty available_time_slots.
• The eligible-participant count is greater than or equal to the cohort's matching_min_group_size (default 4 when NULL).

Always returns 200 with the readiness shape — never returns a 4xx for "not ready" cases. 404 only if the cohort itself doesn't exist.

{
  "success": true
}