feat: mark generated and identity columns across writers and DBML

- bun: scanonly+generated for GENERATED columns; scanonly+identity for ALWAYS identity (PK gets identity only)
- gorm: <-:false+generated / identity, same primary key rule
- dbml: write GENERATED/IDENTITY column notes and read them back into the model
- pgsql: emit generation/identity clauses in migration create-table and add-column, no DEFAULT
- readmes updated

pkg/writers/dbml/writer.go

@@ -114,6 +114,24 @@ func (w *Writer) schemaToDBML(schema *models.Schema) string {
 	return sb.String()
 }
 
+// columnMarkerNote returns the note marking a column the database computes itself
+// (GENERATED ... STORED, or GENERATED ... AS IDENTITY), or "" for an ordinary column.
+// The DBML reader turns the note back into the model's Generated/Identity fields.
+func columnMarkerNote(column *models.Column) string {
+	switch {
+	case column.Generated:
+		return fmt.Sprintf("GENERATED ALWAYS AS (%s) STORED", column.GenerationExpression)
+	case column.Identity && column.IdentityGeneration != "":
+		return fmt.Sprintf("GENERATED %s AS IDENTITY", strings.ToUpper(column.IdentityGeneration))
+	}
+	return ""
+}
+
+// escapeNote escapes a value for use inside a single-quoted DBML note.
+func escapeNote(s string) string {
+	return strings.ReplaceAll(strings.ReplaceAll(s, `\`, `\\`), `'`, `\'`)
+}
+
 // tableToDBML converts a Table to DBML format string
 func (w *Writer) tableToDBML(t *models.Table) string {
 	var sb strings.Builder
@@ -146,6 +164,10 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 			}
 		}
 
+		if marker := columnMarkerNote(column); marker != "" {
+			attrs = append(attrs, fmt.Sprintf("note: '%s'", escapeNote(marker)))
+		}
+
 		if len(attrs) > 0 {
 			fmt.Fprintf(&sb, " [%s]", strings.Join(attrs, ", "))
 		}