feat(auth): 添加免登录切换租户功能

- 新增接口获取当前用户可切换的租户列表，支持手机号和邮箱聚合租户
- 实现免登录切换租户接口，需判断当前用户权限及目标租户状态
- 编写辅助方法查找可切换的用户账户
- 添加将用户信息转换为租户选项的工具方法
- 在切换成功后生成新的访问令牌并保存登录记录

src/main/java/com/gxwebsoft/common/system/controller/MainController.java

@@ -65,6 +65,7 @@ import java.net.URLEncoder;
 import java.text.MessageFormat;
 import java.time.Instant;
 import java.time.LocalDateTime;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -1131,6 +1132,105 @@ public class MainController extends BaseController {
     return success("登录成功", new LoginResult(access_token, user));
   }
 
+  @Operation(summary = "获取当前登录用户可切换的租户列表（免登录切换前置）")
+  @GetMapping("/auth/switchableTenants")
+  public ApiResult<?> switchableTenants() {
+    User current = getLoginUser();
+    if (current == null) {
+      return fail("未登录或登录已过期", null);
+    }
+    List<TenantOption> options = new ArrayList<>();
+    // 按手机号聚合（仅管理员账号）
+    if (StrUtil.isNotBlank(current.getPhone())) {
+      LoginParam phoneParam = new LoginParam();
+      phoneParam.setPhone(current.getPhone());
+      List<User> byPhone = userService.getAdminsByPhone(phoneParam);
+      if (byPhone != null) {
+        for (User u : byPhone) {
+          options.add(toTenantOption(u));
+        }
+      }
+    }
+    // 按邮箱聚合（管理员账号，按租户去重）
+    if (StrUtil.isNotBlank(current.getEmail())) {
+      List<User> byEmail = userService.findAccountsByEmail(current.getEmail());
+      if (byEmail != null) {
+        for (User u : byEmail) {
+          if (!Boolean.TRUE.equals(u.getIsAdmin())) {
+            continue;
+          }
+          final Integer tId = u.getTenantId();
+          if (tId != null && options.stream().noneMatch(o -> tId.equals(o.getTenantId()))) {
+            options.add(toTenantOption(u));
+          }
+        }
+      }
+    }
+    return success(options);
+  }
+
+  @Operation(summary = "免登录切换租户（需已登录，当前用户须为目标租户管理员）")
+  @PostMapping("/auth/switchTenant")
+  public ApiResult<LoginResult> switchTenant(@RequestBody LoginParam param, HttpServletRequest request) {
+    Integer targetTenantId = param.getTenantId();
+    if (targetTenantId == null) {
+      return fail("请选择租户", null);
+    }
+    User current = getLoginUser();
+    if (current == null) {
+      return fail("未登录或登录已过期", null);
+    }
+    // 校验目标租户在可切换范围内（与 switchableTenants 一致）
+    User target = findSwitchableUser(current, targetTenantId);
+    if (target == null) {
+      return fail("无权切换到该租户", null);
+    }
+    if (!target.getStatus().equals(0)) {
+      return fail("该租户账号已被冻结", null);
+    }
+    String access_token = generateToken(target);
+    loginRecordService.saveAsync(target.getUsername(), LoginRecord.TYPE_LOGIN, null, target.getTenantId(), request);
+    return success("切换成功", new LoginResult(access_token, target));
+  }
+
+  private User findSwitchableUser(User current, Integer targetTenantId) {
+    List<User> candidates = new ArrayList<>();
+    if (StrUtil.isNotBlank(current.getPhone())) {
+      LoginParam phoneParam = new LoginParam();
+      phoneParam.setPhone(current.getPhone());
+      List<User> byPhone = userService.getAdminsByPhone(phoneParam);
+      if (byPhone != null) {
+        candidates.addAll(byPhone);
+      }
+    }
+    if (StrUtil.isNotBlank(current.getEmail())) {
+      List<User> byEmail = userService.findAccountsByEmail(current.getEmail());
+      if (byEmail != null) {
+        for (User u : byEmail) {
+          if (Boolean.TRUE.equals(u.getIsAdmin())) {
+            candidates.add(u);
+          }
+        }
+      }
+    }
+    return candidates.stream()
+      .filter(u -> targetTenantId.equals(u.getTenantId()))
+      .findFirst()
+      .orElse(null);
+  }
+
+  private TenantOption toTenantOption(User u) {
+    return new TenantOption(
+      u.getTenantId(),
+      u.getTenantName(),
+      u.getUserId(),
+      u.getUsername(),
+      u.getNickname(),
+      null,
+      u.getAvatar()
+    );
+  }
+
   /**
    * 生成 JWT token 并存入 Redis
    */