fix: Date.Value() returns string to prevent timezone day-shift; add GormDBDataType()

- Date.Value() now returns the date as a string ("YYYY-MM-DD") instead of
  time.Time to prevent database drivers from applying timezone conversions
  that can shift the date by a day.
- Add GormDBDataType() to Date for explicit provider-specific column types
  (date for postgres/mysql/sqlite, DATE for sqlserver).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dannyota

date.go

@@ -3,7 +3,11 @@ package datatypes
 import (
 	"database/sql"
 	"database/sql/driver"
+	"fmt"
 	"time"
+
+	"gorm.io/gorm"
+	"gorm.io/gorm/schema"
 )
 
 type Date time.Time
@@ -17,14 +21,30 @@ func (date *Date) Scan(value interface{}) (err error) {
 
 func (date Date) Value() (driver.Value, error) {
 	y, m, d := time.Time(date).Date()
-	return time.Date(y, m, d, 0, 0, 0, 0, time.Time(date).Location()), nil
+	return fmt.Sprintf("%04d-%02d-%02d", y, m, d), nil
 }
 
 // GormDataType gorm common data type
 func (date Date) GormDataType() string {
 	return "date"
 }
 
+// GormDBDataType gorm db data type
+func (Date) GormDBDataType(db *gorm.DB, field *schema.Field) string {
+	switch db.Dialector.Name() {
+	case "mysql":
+		return "DATE"
+	case "postgres":
+		return "DATE"
+	case "sqlserver":
+		return "DATE"
+	case "sqlite":
+		return "TEXT"
+	default:
+		return ""
+	}
+}
+
 func (date Date) GobEncode() ([]byte, error) {
 	return time.Time(date).GobEncode()
 }