refactor(api): unify typed error contract across draft pricing and publish flows

standardize typed error responses across draft, pricing and publish endpoints

reduce contract drift between related flows
keep client-side handling more predictable and consistent

backend/app/api/routes/pricing.py

@@ -30,6 +30,7 @@ from app.schemas.pricing import (
     PricingCategoryUpdateResponse,
 )
 from app.security.auth import require_api_key
+from app.services.api_errors import raise_unprocessable
 from app.services.draft_guard import validate_expected_draft_version_if_provided
 
 router = APIRouter()
@@ -213,9 +214,10 @@ async def create_price_rule_endpoint(
     try:
         amount = Decimal(payload.amount)
     except Exception:
-        raise HTTPException(
-            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
-            detail="Некорректная сумма",
+        raise_unprocessable(
+            code="invalid_amount",
+            message="Некорректная сумма",
+            amount=payload.amount,
         )
 
     price_rule_id = await create_price_rule(
@@ -273,9 +275,10 @@ async def update_price_rule_endpoint(
     try:
         amount = Decimal(payload.amount)
     except Exception:
-        raise HTTPException(
-            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
-            detail="Некорректная сумма",
+        raise_unprocessable(
+            code="invalid_amount",
+            message="Некорректная сумма",
+            amount=payload.amount,
         )
 
     row = await update_price_rule(