fix: 注册密码改为可选，机器注册无需密码

- RegisterRequest.password 移除 @NotBlank
- 密码为空时自动生成随机密码
- mediabot 只需 email 即可注册获得 apiKey/apiSecret
- 重装后同邮箱重新注册即可，无需记住密码

par-core/src/main/java/com/par/core/dto/RegisterRequest.java

@@ -15,7 +15,6 @@ public class RegisterRequest {
     @Email(message = "邮箱格式不正确")
     private String email;
 
-    @NotBlank(message = "密码不能为空")
     @Size(min = 6, max = 128, message = "密码长度须在 6-128 位之间")
     private String password;
 

par-core/src/main/java/com/par/core/service/impl/AccountServiceImpl.java

@@ -49,7 +49,15 @@ public class AccountServiceImpl implements AccountService {
 
         Account account = new Account();
         account.setEmail(request.getEmail().toLowerCase().trim());
-        account.setPasswordHash(PasswordUtil.encode(request.getPassword()));
+
+        // 密码为空则自动生成（机器注册场景）
+        String password = request.getPassword();
+        if (password == null || password.isBlank()) {
+            byte[] pwdBytes = new byte[16];
+            SECURE_RANDOM.nextBytes(pwdBytes);
+            password = Base64.getUrlEncoder().withoutPadding().encodeToString(pwdBytes);
+        }
+        account.setPasswordHash(PasswordUtil.encode(password));
         account.setDisplayName(request.getDisplayName());
         account.setTrustLevel(TrustLevel.MEMBER);
         account.setIsActive(true);