feat(writers): stamp RelSpec version in generated headers; preserve DBML column order

- Add pkg/buildinfo with Version/BuildDate (set via ldflags, VCS fallback);
  cmd/relspec now sources version info from it
- Emit "RelSpec <version> (built: <date>)" in generated file headers for
  bun, gorm, drizzle, pgsql (incl. migration), mssql, sqlite writers
- pgsql writer: getSortedColumns now sorts by Sequence then Name so the
  streaming WriteSchema/WriteDatabase path preserves source column order
- dbml reader: mergeTable re-bases merged-in column Sequence values past the
  existing max, fixing colliding sequences (and alphabetical fallback) when a
  table is split across multiple DBML files
- Tests for bun/gorm header + column order, and dbml multi-file merge ordering

pkg/writers/pgsql/writer.go

@@ -12,6 +12,7 @@ import (
 	"sync"
 	"time"
 
+	"git.warky.dev/wdevs/relspecgo/pkg/buildinfo"
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
 	"git.warky.dev/wdevs/relspecgo/pkg/pgsql"
 	"git.warky.dev/wdevs/relspecgo/pkg/writers"
@@ -101,7 +102,7 @@ func (w *Writer) WriteDatabase(db *models.Database) error {
 	// Write header comment
 	fmt.Fprintf(w.writer, "-- PostgreSQL Database Schema\n")
 	fmt.Fprintf(w.writer, "-- Database: %s\n", db.Name)
-	fmt.Fprintf(w.writer, "-- Generated by RelSpec\n")
+	fmt.Fprintf(w.writer, "-- Generated by %s\n", buildinfo.GeneratedComment())
 	if w.options.ContinueOnError {
 		fmt.Fprintf(w.writer, "\\set ON_ERROR_STOP off\n")
 	}
@@ -125,7 +126,7 @@ func (w *Writer) GenerateDatabaseStatements(db *models.Database) ([]string, erro
 	// Add header comment
 	statements = append(statements, "-- PostgreSQL Database Schema")
 	statements = append(statements, fmt.Sprintf("-- Database: %s", db.Name))
-	statements = append(statements, "-- Generated by RelSpec")
+	statements = append(statements, "-- Generated by "+buildinfo.GeneratedComment())
 
 	// Process each schema in the database
 	for _, schema := range db.Schemas {
@@ -555,7 +556,7 @@ func (w *Writer) GenerateAddColumnsForDatabase(db *models.Database) ([]string, e
 
 	statements = append(statements, "-- Add missing columns to existing tables")
 	statements = append(statements, fmt.Sprintf("-- Database: %s", db.Name))
-	statements = append(statements, "-- Generated by RelSpec")
+	statements = append(statements, "-- Generated by "+buildinfo.GeneratedComment())
 
 	for _, schema := range db.Schemas {
 		schemaStatements, err := w.GenerateAddColumnStatements(schema)
@@ -1446,19 +1447,10 @@ func (w *Writer) writeComments(schema *models.Schema) error {
 
 // Helper functions
 
-// getSortedColumns returns columns sorted by name
+// getSortedColumns returns columns sorted by Sequence then Name, preserving the
+// original column order from the source schema for deterministic output.
 func getSortedColumns(columns map[string]*models.Column) []*models.Column {
-	names := make([]string, 0, len(columns))
-	for name := range columns {
-		names = append(names, name)
-	}
-	sort.Strings(names)
-
-	sorted := make([]*models.Column, 0, len(columns))
-	for _, name := range names {
-		sorted = append(sorted, columns[name])
-	}
-	return sorted
+	return sortColumns(columns)
 }
 
 // isIntegerType checks if a column type is an integer type