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/convert.go

@@ -33,6 +33,7 @@ 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"
 )
@@ -84,6 +85,7 @@ Output formats:
   - prisma: Prisma schema files (.prisma)
   - typeorm: TypeORM entity files (TypeScript)
   - pgsql: PostgreSQL SQL schema
+  - sqlite: SQLite SQL schema (with automatic schema flattening)
 
 PostgreSQL Connection String Examples:
   postgres://username:password@localhost:5432/database_name
@@ -346,6 +348,9 @@ func writeDatabase(db *models.Database, dbType, outputPath, packageName, schemaF
 	case "pgsql", "postgres", "postgresql", "sql":
 		writer = wpgsql.NewWriter(writerOpts)
 
+	case "sqlite", "sqlite3":
+		writer = wsqlite.NewWriter(writerOpts)
+
 	case "prisma":
 		writer = wprisma.NewWriter(writerOpts)