fix(db): 缩短 license_key 列至 VARCHAR(768) 避免 InnoDB 索引超限 [tsk_Qmk4wT_dkqRR]

原 size:2048 在 utf8mb4 下产生 8192 字节索引，超过 InnoDB 3072 字节上限，
全新环境 AutoMigrate 必失败。改为 VARCHAR(768)（768×4=3072 字节，恰好
在上限内），schema.sql 同步更新列类型并将 uk_license_key 改为全列索引（无
需前缀）。新增测试 TestLicenseTokenFitsColumnLimit 验证最坏情况 token 长度
确实在 768 字符以内。

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

backend/internal/model/license.go

@@ -5,7 +5,7 @@ import "time"
 type License struct {
 	Base
 	ShopID     uint64     `gorm:"not null;index" json:"shop_id"`
-	LicenseKey string     `gorm:"size:2048;uniqueIndex" json:"license_key"`
+	LicenseKey string     `gorm:"size:768;uniqueIndex" json:"license_key"`
 	Type       string     `gorm:"type:enum('trial','monthly','annual','lifetime');default:'trial'" json:"type"`
 	ExpiresAt  *time.Time `json:"expires_at"`
 	IsActive   bool       `gorm:"default:true" json:"is_active"`

backend/internal/util/license_key_test.go

@@ -73,3 +73,38 @@ func TestVerifyLicenseToken_InvalidFormat(t *testing.T) {
 	_, err = VerifyLicenseToken("not-a-valid-token", pub)
 	assert.ErrorIs(t, err, ErrInvalidLicenseToken)
 }
+
+// TestLicenseTokenFitsColumnLimit verifies that a realistic (even worst-case)
+// license token fits within the VARCHAR(768) column limit imposed by the
+// InnoDB index constraint (768 chars × 4 bytes/char = 3072 bytes max).
+func TestLicenseTokenFitsColumnLimit(t *testing.T) {
+	const columnLimit = 768
+
+	priv, _, err := GenerateEd25519KeyPair()
+	require.NoError(t, err)
+
+	// Use a large features map to simulate a worst-case payload.
+	exp := time.Now().Add(365 * 24 * time.Hour).Unix()
+	payload := LicensePayload{
+		ShopID:    999999999,
+		LicenseID: 999999999,
+		Type:      "lifetime",
+		IssuedAt:  time.Now().Unix(),
+		ExpiresAt: &exp,
+		MaxDevices: 99,
+		Features: map[string]any{
+			"finance":    true,
+			"inventory":  true,
+			"reports":    true,
+			"export":     true,
+			"multi_shop": true,
+			"api_access": true,
+		},
+	}
+
+	token, err := IssueLicenseToken(payload, priv)
+	require.NoError(t, err)
+
+	assert.LessOrEqual(t, len(token), columnLimit,
+		"license token length %d exceeds VARCHAR(%d) column limit", len(token), columnLimit)
+}

backend/schema/schema.sql

@@ -58,7 +58,7 @@ CREATE TABLE IF NOT EXISTS `users` (
 CREATE TABLE IF NOT EXISTS `licenses` (
   `id`           BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
   `shop_id`      BIGINT UNSIGNED NOT NULL,
-  `license_key`  VARCHAR(2048)   NOT NULL COMMENT 'Ed25519 signed token',
+  `license_key`  VARCHAR(768)    NOT NULL COMMENT 'Ed25519 signed token',
   `device_id`    VARCHAR(255)    DEFAULT NULL COMMENT 'deprecated: use license_devices',
   `type`         ENUM('trial','monthly','annual','lifetime') NOT NULL DEFAULT 'trial',
   `expires_at`   DATETIME        DEFAULT NULL COMMENT 'NULL=永久',
@@ -69,7 +69,7 @@ CREATE TABLE IF NOT EXISTS `licenses` (
   `created_at`   DATETIME        NOT NULL DEFAULT CURRENT_TIMESTAMP,
   `updated_at`   DATETIME        NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
   PRIMARY KEY (`id`),
-  UNIQUE KEY `uk_license_key` (`license_key`(255)),
+  UNIQUE KEY `uk_license_key` (`license_key`),
   KEY `idx_shop_id` (`shop_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='许可证';