fix: writer/reader correctness and determinism issues

- merge: cloneTable keeps relationships; skip-tables applies to new schemas
- diff: detect schema description/owner changes
- prisma: reader no longer turns relation fields into columns, enum
  detection via declared names; writer type mapping is ordered
- typeorm writer: keep explicit SQL types that cannot be inferred
- drizzle: enum columns call the enum constant; reader resolves them
- mysql/mssql/sqlite writers: honour OutputPath, deterministic column
  and constraint order; mssql live execute covers full schema
- template: ToYAML recovers from panics; Merge nil-pointer loop
- regenerate drizzle fixtures

pkg/writers/template/safe_access.go

@@ -101,11 +101,8 @@ func Merge(maps ...interface{}) map[interface{}]interface{} {
 	for _, m := range maps {
 		v := reflect.ValueOf(m)
 
-		// Dereference pointers
-		for v.Kind() == reflect.Pointer {
-			if v.IsNil() {
-				continue
-			}
+		// Dereference pointers; a nil pointer contributes nothing
+		for v.Kind() == reflect.Pointer && !v.IsNil() {
 			v = v.Elem()
 		}