feat(admin): add comprehensive admin management system

- Add admin handlers and services for users, posts, comments, groups, and dashboard
- Implement role permission management with ability to view and update permissions
- Add database seeding for roles and Casbin permission policies
- Upgrade Casbin from v2 to v3 with GORM adapter for persistent policy storage
- Add admin-specific repository methods with filtering and pagination
- Register new admin API routes under /api/v1/admin/*

internal/handler/admin_user_handler.go

@@ -0,0 +1,105 @@
+package handler
+
+import (
+	"strconv"
+
+	"carrot_bbs/internal/dto"
+	"carrot_bbs/internal/model"
+	"carrot_bbs/internal/pkg/response"
+	"carrot_bbs/internal/service"
+
+	"github.com/gin-gonic/gin"
+)
+
+// AdminUserHandler 管理端用户处理器
+type AdminUserHandler struct {
+	adminUserService service.AdminUserService
+}
+
+// NewAdminUserHandler 创建管理端用户处理器
+func NewAdminUserHandler(adminUserService service.AdminUserService) *AdminUserHandler {
+	return &AdminUserHandler{
+		adminUserService: adminUserService,
+	}
+}
+
+// GetUserList 获取用户列表
+// GET /api/v1/admin/users
+func (h *AdminUserHandler) GetUserList(c *gin.Context) {
+	// 解析分页参数
+	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
+	pageSize, _ := strconv.Atoi(c.DefaultQuery("page_size", "20"))
+
+	if page <= 0 {
+		page = 1
+	}
+	if pageSize <= 0 || pageSize > 100 {
+		pageSize = 20
+	}
+
+	// 获取筛选参数
+	keyword := c.Query("keyword")
+	status := c.Query("status")
+
+	// 验证状态参数
+	if status != "" && status != string(model.UserStatusActive) && status != string(model.UserStatusBanned) {
+		response.BadRequest(c, "invalid status value")
+		return
+	}
+
+	users, total, err := h.adminUserService.GetUserList(c.Request.Context(), page, pageSize, keyword, status)
+	if err != nil {
+		response.InternalServerError(c, "failed to get user list")
+		return
+	}
+
+	response.Paginated(c, users, total, page, pageSize)
+}
+
+// GetUserDetail 获取用户详情
+// GET /api/v1/admin/users/:id
+func (h *AdminUserHandler) GetUserDetail(c *gin.Context) {
+	userID := c.Param("id")
+	if userID == "" {
+		response.BadRequest(c, "user id is required")
+		return
+	}
+
+	userDetail, err := h.adminUserService.GetUserDetail(c.Request.Context(), userID)
+	if err != nil {
+		response.NotFound(c, "user not found")
+		return
+	}
+
+	response.Success(c, userDetail)
+}
+
+// UpdateUserStatus 更新用户状态
+// PUT /api/v1/admin/users/:id/status
+func (h *AdminUserHandler) UpdateUserStatus(c *gin.Context) {
+	userID := c.Param("id")
+	if userID == "" {
+		response.BadRequest(c, "user id is required")
+		return
+	}
+
+	var req dto.AdminUpdateUserStatusRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "invalid request body: "+err.Error())
+		return
+	}
+
+	// 验证状态值
+	if req.Status != string(model.UserStatusActive) && req.Status != string(model.UserStatusBanned) {
+		response.BadRequest(c, "invalid status value, must be 'active' or 'banned'")
+		return
+	}
+
+	userDetail, err := h.adminUserService.UpdateUserStatus(c.Request.Context(), userID, model.UserStatus(req.Status))
+	if err != nil {
+		response.HandleError(c, err, "failed to update user status")
+		return
+	}
+
+	response.Success(c, userDetail)
+}