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/drizzle/template_data.go

@@ -4,14 +4,16 @@ import (
 	"sort"
 	"strings"
 
+	"git.warky.dev/wdevs/relspecgo/pkg/buildinfo"
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
 )
 
 // TemplateData represents the data passed to the template for code generation
 type TemplateData struct {
-	Imports []string
-	Enums   []*EnumData
-	Tables  []*TableData
+	GeneratedBy string
+	Imports     []string
+	Enums       []*EnumData
+	Tables      []*TableData
 }
 
 // EnumData represents an enum in the schema
@@ -59,7 +61,8 @@ type IndexData struct {
 // NewTemplateData creates a new TemplateData
 func NewTemplateData() *TemplateData {
 	return &TemplateData{
-		Imports: make([]string, 0),
+		GeneratedBy: buildinfo.GeneratedComment(),
+		Imports:     make([]string, 0),
 		Enums:   make([]*EnumData, 0),
 		Tables:  make([]*TableData, 0),
 	}