Manually re-send a product fulfillment email to a buyer. Used when the original send failed (e.g., the SKU wasn't registered in PRODUCT_INFO at purchase time). Token + amount are pulled from customers.jsonl by session_id; pass the session_id in the body.

Optional to_email: the buyer mistyped their address at checkout. Delegates to buyer_email.correct_purchase_email — the same path the buyer-facing /api/checkout/fix-email uses — which records a fresh token under the corrected address with the SAME session_id (no revenue double-count) and sends the fulfillment email there.