fix(头像生成): 当邮箱为空时使用昵称生成头像哈希

修复 getCravatar 函数在邮箱为空时无法生成有效头像的问题。现在当邮箱为空或不存在时，函数会尝试使用昵称作为替代标识符生成 MD5 哈希。如果两者都不可用，则返回默认占位符头像，确保始终返回有效的头像 URL。

cwd-api/src/api/admin/listComments.ts

@@ -65,7 +65,7 @@ export const listComments = async (c: Context<{ Bindings: Bindings }>) => {
 					? row.likes
 					: 0,
 			ua: row.ua,
-			avatar: await getCravatar(row.email, avatarPrefix || undefined),
+			avatar: await getCravatar(row.email, row.name, avatarPrefix || undefined),
 			isAdmin: adminEmail && row.email === adminEmail
 		}))
 	);

cwd-api/src/api/public/getComments.ts

@@ -69,7 +69,7 @@ export const getComments = async (c: Context<{ Bindings: Bindings }>) => {
     // 2. 批量处理头像并格式化
     const allComments = await Promise.all(results.map(async (row: any) => ({
       ...row,
-      avatar: await getCravatar(row.email, avatar_prefix || undefined),
+      avatar: await getCravatar(row.email, row.name, avatar_prefix || undefined),
       isAdmin: adminEmail && row.email === adminEmail,
       replies: []
     })))