feat(sqlite): add SQLite writer for converting PostgreSQL schemas

- Implement SQLite DDL writer to convert PostgreSQL schemas to SQLite-compatible SQL statements.
- Include automatic schema flattening, type mapping, auto-increment detection, and function translation.
- Add templates for creating tables, indexes, unique constraints, check constraints, and foreign keys.
- Implement tests for writer functionality and data type mapping.

cmd/relspec/merge.go

@@ -34,6 +34,7 @@ import (
 	wjson "git.warky.dev/wdevs/relspecgo/pkg/writers/json"
 	wpgsql "git.warky.dev/wdevs/relspecgo/pkg/writers/pgsql"
 	wprisma "git.warky.dev/wdevs/relspecgo/pkg/writers/prisma"
+	wsqlite "git.warky.dev/wdevs/relspecgo/pkg/writers/sqlite"
 	wtypeorm "git.warky.dev/wdevs/relspecgo/pkg/writers/typeorm"
 	wyaml "git.warky.dev/wdevs/relspecgo/pkg/writers/yaml"
 )
@@ -385,6 +386,8 @@ func writeDatabaseForMerge(dbType, filePath, connString string, db *models.Datab
 			return fmt.Errorf("%s: file path is required for TypeORM format", label)
 		}
 		writer = wtypeorm.NewWriter(&writers.WriterOptions{OutputPath: filePath, FlattenSchema: flattenSchema})
+	case "sqlite", "sqlite3":
+		writer = wsqlite.NewWriter(&writers.WriterOptions{OutputPath: filePath, FlattenSchema: flattenSchema})
 	case "pgsql":
 		writerOpts := &writers.WriterOptions{OutputPath: filePath, FlattenSchema: flattenSchema}
 		if connString != "" {