fix: replace margin/fulfilment prompt with answerable wording

The "Where am I losing margin — biggest discounts, highest refunds,
longest fulfilment times?" example asked for two dimensions Hey Woo
can't actually answer: true margin needs COGS data the catalog
doesn't carry, and fulfilment-time analysis needs order status-
transition or shipping timestamps the analytics surface explicitly
says are unavailable.

Reframed to dimensions Hey Woo's tools genuinely cover: biggest
discounts (coupon-performance), biggest refunds (refund-analysis),
and oldest on-hold or failed orders (orders_summary filtered by
status). Same merchant intent, an answer Claude can actually give.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: garysmurray

docs/prompt-guides.md

@@ -39,7 +39,7 @@ What's bleeding today.
 
 - *"What's stuck in fulfillment? Show on-hold orders by age and any failed orders from the last 30 days."*
 - *"Which top sellers are running low or out based on sales velocity?"*
-- *"Where am I losing margin — biggest discounts, highest refunds, longest fulfilment times?"*
+- *"Where's the leakage right now — biggest discounts, biggest refunds, and oldest on-hold or failed orders worth chasing?"*
 
 ## 5. Tune up the catalog