feat(dbml): @postgres/@sqlite dialect directives (#19)

Add parseable `@<namespace>[(<target>)]: <args>` directives embedded in DBML.
They are stored losslessly on each object's Metadata, round-trip unchanged
through the DBML writer, and are translated to SQL only by the writer for the
matching dialect.

- models: Directive type + catalog; Metadata map added to Column and Index
- dbml reader: parse and attach directives at database/table/column/index
  level; line-numbered errors; repeatable by default with singleton duplicate
  detection. Fixes a preexisting bug where an `indexes {}` closing brace ended
  the table early, dropping trailing Note: and directive lines.
- dbml writer: re-emit directives at their location; idempotent output
- pgsql writer: PARTITION BY / INHERITS / WITH / TABLESPACE (table),
  STORAGE / COMPRESSION / identity (column), WITH / TABLESPACE (index)
- sqlite writer: WITHOUT ROWID / STRICT (table), COLLATE (column)
- --strict-directives flag on ReaderOptions and WriterOptions
- docs/DBML_DIRECTIVES.md + reader/writer READMEs

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ss2MY5J11cRGwEz86ZXk7d

pkg/readers/dbml/reader.go

@@ -435,11 +435,14 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 	var inIndexes bool
 	var inTable bool
 	var columnSeq uint
+	var lastIndex *models.Index // most recent index in the current Indexes block
+	lineNo := 0
 
 	tableRegex := regexp.MustCompile(`^Table\s+(.+?)\s*{`)
 	refRegex := regexp.MustCompile(`^Ref:\s+(.+)`)
 
 	for scanner.Scan() {
+		lineNo++
 		line := strings.TrimSpace(scanner.Text())
 
 		// Skip empty lines and comments
@@ -447,6 +450,20 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 			continue
 		}
 
+		// Parse a dialect directive (@postgres:, @sqlite:, …). Handled before
+		// table/column/index parsing so directive lines are never mistaken for
+		// columns.
+		if strings.HasPrefix(line, "@") {
+			pd, err := parseDirectiveLine(line, lineNo)
+			if err != nil {
+				return nil, err
+			}
+			if err := r.attachDirective(pd, db, currentTable, inTable, inIndexes, lastIndex); err != nil {
+				return nil, err
+			}
+			continue
+		}
+
 		// Parse Table definition
 		if matches := tableRegex.FindStringSubmatch(line); matches != nil {
 			tableName := matches[1]
@@ -474,8 +491,10 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 			continue
 		}
 
-		// End of table definition
-		if inTable && line == "}" {
+		// End of table definition. Guarded by !inIndexes so the closing brace
+		// of an `indexes { }` block is not mistaken for the end of the table
+		// (which would drop any table-level content that follows it).
+		if inTable && !inIndexes && line == "}" {
 			if currentTable != nil && currentSchema != "" {
 				schemaMap[currentSchema].Tables = append(schemaMap[currentSchema].Tables, currentTable)
 				currentTable = nil
@@ -488,12 +507,14 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 		// Parse indexes section
 		if inTable && (strings.HasPrefix(line, "Indexes {") || strings.HasPrefix(line, "indexes {")) {
 			inIndexes = true
+			lastIndex = nil
 			continue
 		}
 
 		// End of indexes section
 		if inIndexes && line == "}" {
 			inIndexes = false
+			lastIndex = nil
 			continue
 		}
 
@@ -513,6 +534,7 @@ func (r *Reader) parseDBML(content string) (*models.Database, error) {
 			index := r.parseIndex(line, currentTable.Name, currentSchema)
 			if index != nil {
 				currentTable.Indexes[index.Name] = index
+				lastIndex = index
 			}
 			continue
 		}