feat(price): detect quantity discounts via baseprice, show Disc. badge

GoMag sends baseprice (catalog price) alongside price (discounted).
When baseprice > price, the item is volume-discounted — skip ROA
price comparison and show amber "Disc." badge instead of false
mismatch. Strikethrough baseprice in price column for transparency.

Pipeline: parse baseprice → store in SQLite → skip in validation →
pass flag to frontend → render badge (desktop + mobile pill badge
with aria-label, opacity 0.6 for dark mode).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

api/app/routers/sync.py

@@ -465,6 +465,9 @@ async def order_detail(order_number: str):
                 item["price_match"] = pi.get("match")
                 if pi.get("kit"):
                     item["kit"] = True
+                if pi.get("quantity_discount"):
+                    item["quantity_discount"] = True
+                    item["baseprice"] = pi.get("baseprice")
         order_price_check = price_data.get("summary", {})
         # Cache price_match in SQLite if changed
         if order_price_check.get("oracle_available") is not False: