Support pipeline DSL modification through dataset configuration (backend) (#16991)

…end)

### Summary

Support pipeline DSL modification through dataset configuration
(backend)

Key modification: knowledgebase.parser_config

---------

Co-authored-by: yzc <yuzhichang@gmail.com>

internal/parser/parser/csv_parser.go

@@ -126,9 +126,10 @@ func (p *CSVParser) ParseWithResult(filename string, data []byte) ParseResult {
 	case "", "csv":
 		// Continue with the local CSV parser.
 	default:
-		return ParseResult{
-			Err: fmt.Errorf("unsupported CSV parse method: %q", p.ParseMethod),
-		}
+		// PDF-specific methods like "DeepDOC" / "PaddleOCR" / "MinerU"
+		// are meaningless for CSV; treat them as the default CSV path,
+		// matching Python's behaviour where parse_method is irrelevant
+		// for CSV processing.
 	}
 
 	text := string(data)
@@ -147,6 +148,7 @@ func (p *CSVParser) ParseWithResult(filename string, data []byte) ParseResult {
 	reader := csv.NewReader(strings.NewReader(text))
 	reader.LazyQuotes = true
 	reader.TrimLeadingSpace = true
+	reader.FieldsPerRecord = -1 // Allow variable column counts, matching Python csv.reader behaviour.
 
 	records, err := reader.ReadAll()
 	if err != nil {