feat: 新增 SQLite3 虚拟表框架及方言扩展

- 新增 dialect/sqlite3/vtab 包，提供干净的虚拟表接口（Module/Table/Cursor）
- 适配层自动将 BestIndex 约束与 Filter 值绑定（ConstraintInfo.Value），无需手动编解码 IdxStr
- 支持 OpLIMIT/OpOFFSET 约束下推
- 新增 SupportsDistinct 方言选项，控制 SELECT 级和表达式级 DISTINCT 生成
- sqlite3 方言注册 IF() 函数支持

schema/dialect/sqlite3/sqlite3.go

@@ -13,7 +13,7 @@ import (
 )
 
 var (
-	sqlite3DefaultModifiers = []string{"VirtualAs", "StoredAs", "Nullable", "Default", "Increment"}
+	sqlite3DefaultModifiers = []string{"VirtualAs", "StoredAs", "Hidden", "Nullable", "Default", "Increment"}
 	sqlite3Serials          = []string{"bigInteger", "integer", "mediumInteger", "smallInteger", "tinyInteger"}
 )
 
@@ -178,8 +178,13 @@ func (this Sqlite3) GetColumnModifier(modifier string, bp *schema.Blueprint, col
 		if v := column.GetStoredAs(); v != "" {
 			return this.GenerateSQL(" GENERATED ALWAYS AS (?) STORED", db.L(v))
 		}
+	case "Hidden":
+		if column.IsHidden() {
+			return "HIDDEN"
+		}
 	case "Nullable":
-		if column.GetVirtualAs() == "" && column.GetStoredAs() == "" {
+		// HIDDEN 列和生成列不加 NULL/NOT NULL
+		if column.GetVirtualAs() == "" && column.GetStoredAs() == "" && !column.IsHidden() {
 			if column.IsNullable() {
 				return "NULL"
 			}
@@ -267,10 +272,13 @@ func (this Sqlite3) GenerateSQL(sql string, args ...any) string {
 }
 
 func init() {
-	schema.RegisterDialect("sqlite3", func(db *db.Database) schema.Schema {
+	sc := func(db *db.Database) schema.Schema {
 		return &Sqlite3{
 			db:  db,
 			esg: sqlgen.NewExpressionSQLGenerator("sqlite3", sqlite3.DialectOptions()),
 		}
-	})
+	}
+
+	schema.RegisterDialect("sqlite3", sc)
+	schema.RegisterDialect("vtable", sc)
 }

schema/dialect/sqlite3/sqlite3_test.go

@@ -178,6 +178,32 @@ func (t *sqlite3Test) TestCompileDropIfExists() {
 	t.T().Log(sql)
 }
 
+// HIDDEN 列（虚拟表参数列）
+func (t *sqlite3Test) TestCompileCreate_HiddenColumn() {
+	bp := schema.NewBlueprint("api_users")
+	bp.Create()
+
+	bp.BigIncrements("id").AutoIncrement()
+	bp.String("name", 100).Nullable()
+	bp.Integer("age")
+	bp.String("token", 255).Hidden().Nullable()
+	bp.Integer("page_size").Hidden().Nullable()
+
+	sql := t.schema.CompileCreate(bp)
+
+	t.Equal([]string{
+		"CREATE TABLE IF NOT EXISTS `api_users` (\n" +
+			"`id` INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT\n" +
+			"`name` varchar(100) NULL\n" +
+			"`age` INTEGER(0) NOT NULL\n" +
+			"`token` varchar(255) HIDDEN\n" +
+			"`page_size` INTEGER(0) HIDDEN\n" +
+			")",
+	}, sql)
+
+	t.T().Log(sql)
+}
+
 // 表重命名
 func (t *sqlite3Test) TestCompileRename() {
 	bp := schema.NewBlueprint("users")