feat(order-detail): show CODMAT for direct SKUs + mapping validations

- Enrich order detail items with NOM_ARTICOLE data for direct SKUs
  (SKU=CODMAT) that have no ARTICOLE_TERTI entry
- Validate CODMAT exists in nomenclator before saving mapping (400)
- Block redundant self-mapping when SKU is already direct CODMAT (409)
- Show "direct" badge in CODMAT column for direct SKUs
- Show info alert in quick map modal for direct SKUs
- Display backend validation errors inline in modal

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/services/mapping_service.py

@@ -159,6 +159,24 @@ def create_mapping(sku: str, codmat: str, cantitate_roa: float = 1, procent_pret
 
     with database.pool.acquire() as conn:
         with conn.cursor() as cur:
+            # Validate CODMAT exists in NOM_ARTICOLE
+            cur.execute("""
+                SELECT COUNT(*) FROM NOM_ARTICOLE
+                WHERE codmat = :codmat AND sters = 0 AND inactiv = 0
+            """, {"codmat": codmat})
+            if cur.fetchone()[0] == 0:
+                raise HTTPException(status_code=400, detail="CODMAT-ul nu exista in nomenclator")
+
+            # Warn if SKU is already a direct CODMAT in NOM_ARTICOLE
+            if sku == codmat:
+                cur.execute("""
+                    SELECT COUNT(*) FROM NOM_ARTICOLE
+                    WHERE codmat = :sku AND sters = 0 AND inactiv = 0
+                """, {"sku": sku})
+                if cur.fetchone()[0] > 0:
+                    raise HTTPException(status_code=409,
+                                        detail="SKU-ul exista direct in nomenclator ca CODMAT, nu necesita mapare")
+
             # Check for active duplicate
             cur.execute("""
                 SELECT COUNT(*) FROM ARTICOLE_TERTI