Validate which payments can receive notification emails.

This is a lightweight endpoint that checks payment eligibility without actually sending emails. Returns categorized lists of eligible, ineligible, and already-notified payments.

Args: payment_ids: List of payment IDs to validate (optional if filters provided) filters: Filter criteria to fetch payment IDs (optional if payment_ids provided) user_id: ID of the authenticated user (from auth middleware) org_id: ID of the user's organization (from auth middleware)

Returns: dict: Lists of eligible_ids, ineligible_ids (with reasons), and already_notified_ids