feat(05-02): add lagoon.Validate rule-string engine

- Translate Laravel rule strings onto validator.Var and unique:table
- Custom money range via big.Rat; unique checks skip soft-deleted rows
- Fill zeros nil values and Scans jsonable columns

lagoon/fill.go

@@ -1,6 +1,8 @@
 package lagoon
 
 import (
+	"database/sql"
+	"encoding/json"
 	"fmt"
 	"log/slog"
 	"reflect"
@@ -95,8 +97,11 @@ func setField(field reflect.Value, val any) error {
 		return fmt.Errorf("field cannot be set")
 	}
 	if val == nil {
-		if field.Kind() == reflect.Ptr {
-			field.Set(reflect.Zero(field.Type()))
+		field.Set(reflect.Zero(field.Type()))
+		if field.CanAddr() {
+			if scanner, ok := field.Addr().Interface().(sql.Scanner); ok {
+				return scanner.Scan(nil)
+			}
 		}
 		return nil
 	}
@@ -113,11 +118,33 @@ func setField(field reflect.Value, val any) error {
 		return nil
 	}
 	converted, err := convertValue(src, field.Type())
-	if err != nil {
-		return err
+	if err == nil {
+		field.Set(converted)
+		return nil
+	}
+	if field.CanAddr() {
+		if scanner, ok := field.Addr().Interface().(sql.Scanner); ok {
+			scanSrc, scanErr := fillScanSource(val)
+			if scanErr != nil {
+				return scanErr
+			}
+			return scanner.Scan(scanSrc)
+		}
+	}
+	return err
+}
+
+func fillScanSource(val any) (any, error) {
+	switch v := val.(type) {
+	case string, []byte:
+		return v, nil
+	default:
+		b, err := json.Marshal(v)
+		if err != nil {
+			return nil, err
+		}
+		return b, nil
 	}
-	field.Set(converted)
-	return nil
 }
 
 func convertValue(src reflect.Value, destType reflect.Type) (reflect.Value, error) {