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/readers/dbml/reader.go

@@ -804,7 +804,9 @@ func (r *Reader) parseColumn(line, tableName, schemaName string) (*models.Column
 			} else if strings.HasPrefix(attr, "note:") {
 				// Parse column note/comment
 				note := strings.TrimSpace(strings.TrimPrefix(attr, "note:"))
-				column.Comment = strings.Trim(note, "'\"")
+				if !applyColumnMarkerNote(column, note) {
+					column.Comment = strings.Trim(note, "'\"")
+				}
 			} else if strings.HasPrefix(attr, "ref:") {
 				// Parse inline reference
 				// DBML semantics depend on context: