fix(httpapi): stable problem details for client errors

Стабильные detail для 4xx (store, CDN preview, CSV); логирование на сервере. Расширен lint-httpapi для ERR-01 в 4xx.

Co-authored-by: Cursor <[email protected]>

internal/httpapi/problem.go

@@ -7,8 +7,12 @@ import (
 )
 
 const (
-	internalErrorDetail = "an internal error occurred"
-	badGatewayDetail    = "upstream request failed"
+	internalErrorDetail  = "an internal error occurred"
+	badGatewayDetail     = "upstream request failed"
+	notFoundDetail       = "resource not found"
+	invalidInputDetail   = "invalid request data"
+	cdnExtractDetail     = "could not extract prefixes from source"
+	csvInvalidRowDetail  = "invalid row in csv file"
 )
 
 // Problem is RFC 9457 application/problem+json.