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/gorm/writer_test.go

@@ -112,6 +112,46 @@ func TestWriter_WriteTable_MultilineDescriptionProducesValidGo(t *testing.T) {
 	}
 }
 
+func TestWriter_WriteTable_ColumnOrderFollowsSequence(t *testing.T) {
+	// Column.Sequence carries the source (e.g. DBML) declaration order; the
+	// generated struct fields must follow it, not fall back to alphabetical.
+	table := models.InitTable("widget", "public")
+	table.Columns["zeta"] = &models.Column{Name: "zeta", Type: "varchar", Length: 50, Sequence: 1}
+	table.Columns["alpha"] = &models.Column{Name: "alpha", Type: "bigint", NotNull: true, IsPrimaryKey: true, AutoIncrement: true, Sequence: 2}
+	table.Columns["mid_field"] = &models.Column{Name: "mid_field", Type: "integer", Sequence: 3}
+	table.Columns["beta"] = &models.Column{Name: "beta", Type: "varchar", Length: 100, Sequence: 4}
+
+	outputPath := filepath.Join(t.TempDir(), "widget.go")
+	writer := NewWriter(&writers.WriterOptions{OutputPath: outputPath, PackageName: "models"})
+	if err := writer.WriteTable(table); err != nil {
+		t.Fatalf("WriteTable() error = %v", err)
+	}
+
+	generated, err := os.ReadFile(outputPath)
+	if err != nil {
+		t.Fatalf("failed to read generated code: %v", err)
+	}
+	src := string(generated)
+	if _, err := parser.ParseFile(token.NewFileSet(), outputPath, generated, parser.AllErrors); err != nil {
+		t.Fatalf("generated code is invalid Go: %v\n%s", err, src)
+	}
+
+	positions := make([]int, 0, 4)
+	for _, field := range []string{"Zeta ", "Alpha ", "MidField ", "Beta "} {
+		idx := strings.Index(src, "\t"+field)
+		if idx < 0 {
+			t.Fatalf("field %q missing from generated struct:\n%s", field, src)
+		}
+		positions = append(positions, idx)
+	}
+	for i := 1; i < len(positions); i++ {
+		if positions[i] <= positions[i-1] {
+			t.Errorf("struct fields not in Sequence order (want zeta, alpha, mid_field, beta):\n%s", src)
+			break
+		}
+	}
+}
+
 func TestWriter_WriteDatabase_MultiFile(t *testing.T) {
 	// Create a database with two tables
 	db := models.InitDatabase("testdb")