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/database.py

@@ -169,6 +169,7 @@ CREATE TABLE IF NOT EXISTS order_items (
     product_name   TEXT,
     quantity       REAL,
     price          REAL,
+    baseprice      REAL,
     vat            REAL,
     mapping_status TEXT,
     codmat         TEXT,
@@ -357,6 +358,14 @@ def init_sqlite():
                 conn.execute(f"ALTER TABLE orders ADD COLUMN {col} {typedef}")
                 logger.info(f"Migrated orders: added column {col}")
 
+        # Migrate order_items: add baseprice column
+        cursor = conn.execute("PRAGMA table_info(order_items)")
+        oi_cols = {row[1] for row in cursor.fetchall()}
+        if "baseprice" not in oi_cols:
+            conn.execute("ALTER TABLE order_items ADD COLUMN baseprice REAL")
+            conn.execute("UPDATE orders SET price_match = NULL WHERE price_match = 0")
+            logger.info("Migrated order_items: added baseprice; reset price_match for re-check")
+
         conn.commit()
 
         # Backfill address_mismatch from stored address JSON