feat: add --type-map to override SQL-to-Go types in bun and gorm writers

Adds WriterOptions.TypeMappings and a repeatable --type-map sqltype=gotype
flag. Defaults are unchanged when no mapping is given. Closes #36 (bun/gorm).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pkg/writers/gorm/writer.go

@@ -28,6 +28,8 @@ func NewWriter(options *writers.WriterOptions) *Writer {
 		config:     LoadMethodConfigFromMetadata(options.Metadata),
 	}
 
+	w.typeMapper.SetTypeMappings(options.TypeMappings)
+
 	// Initialize templates
 	tmpl, err := NewTemplates()
 	if err != nil {