feat: Implement User Management API (Issue #6) and wire up router

- Create UserService with CRUD operations
- Implement ListUsers with pagination
- Implement GetUser, CreateUser, UpdateUser, DeleteUser
- Add ResetUserPassword for admin password resets
- Create UserHandler with HTTP endpoints
- Update router to wire up all handlers and middleware
- Add authentication middleware to protected routes
- Add admin-only middleware to user management routes

Closes #6

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/internal/api/handlers/users.go

@@ -0,0 +1,224 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/yourusername/victorialogs-manager/internal/services"
+)
+
+// UserHandler handles user management endpoints
+type UserHandler struct {
+	userService *services.UserService
+}
+
+// NewUserHandler creates a new user handler
+func NewUserHandler(userService *services.UserService) *UserHandler {
+	return &UserHandler{
+		userService: userService,
+	}
+}
+
+// ListUsers returns a paginated list of users
+// @Summary List users
+// @Description Get paginated list of users (admin only)
+// @Tags users
+// @Produce json
+// @Param limit query int false "Limit" default(20)
+// @Param offset query int false "Offset" default(0)
+// @Success 200 {object} services.ListUsersResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users [get]
+func (h *UserHandler) ListUsers(c *gin.Context) {
+	var req services.ListUsersRequest
+	if err := c.ShouldBindQuery(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "invalid request",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	resp, err := h.userService.ListUsers(c.Request.Context(), &req)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, ErrorResponse{
+			Error:   "failed to list users",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, resp)
+}
+
+// GetUser returns a user by ID
+// @Summary Get user
+// @Description Get user by ID (admin only)
+// @Tags users
+// @Produce json
+// @Param id path string true "User ID"
+// @Success 200 {object} models.User
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Failure 404 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users/{id} [get]
+func (h *UserHandler) GetUser(c *gin.Context) {
+	id := c.Param("id")
+
+	user, err := h.userService.GetUser(c.Request.Context(), id)
+	if err != nil {
+		c.JSON(http.StatusNotFound, ErrorResponse{
+			Error:   "user not found",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, user)
+}
+
+// CreateUser creates a new user
+// @Summary Create user
+// @Description Create a new user (admin only)
+// @Tags users
+// @Accept json
+// @Produce json
+// @Param request body services.CreateUserRequest true "User data"
+// @Success 201 {object} models.User
+// @Failure 400 {object} ErrorResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users [post]
+func (h *UserHandler) CreateUser(c *gin.Context) {
+	var req services.CreateUserRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "invalid request",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	user, err := h.userService.CreateUser(c.Request.Context(), &req)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "failed to create user",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusCreated, user)
+}
+
+// UpdateUser updates a user
+// @Summary Update user
+// @Description Update user information (admin only)
+// @Tags users
+// @Accept json
+// @Produce json
+// @Param id path string true "User ID"
+// @Param request body services.UpdateUserRequest true "User data"
+// @Success 200 {object} models.User
+// @Failure 400 {object} ErrorResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Failure 404 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users/{id} [put]
+func (h *UserHandler) UpdateUser(c *gin.Context) {
+	id := c.Param("id")
+
+	var req services.UpdateUserRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "invalid request",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	user, err := h.userService.UpdateUser(c.Request.Context(), id, &req)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "failed to update user",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, user)
+}
+
+// DeleteUser deletes a user
+// @Summary Delete user
+// @Description Delete a user (admin only)
+// @Tags users
+// @Produce json
+// @Param id path string true "User ID"
+// @Success 200 {object} SuccessResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Failure 404 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users/{id} [delete]
+func (h *UserHandler) DeleteUser(c *gin.Context) {
+	id := c.Param("id")
+
+	err := h.userService.DeleteUser(c.Request.Context(), id)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "failed to delete user",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, SuccessResponse{
+		Message: "user deleted successfully",
+	})
+}
+
+// ResetUserPassword resets a user's password
+// @Summary Reset user password
+// @Description Reset a user's password (admin only)
+// @Tags users
+// @Accept json
+// @Produce json
+// @Param id path string true "User ID"
+// @Param request body services.ResetPasswordRequest true "New password"
+// @Success 200 {object} SuccessResponse
+// @Failure 400 {object} ErrorResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Security BearerAuth
+// @Router /api/v1/users/{id}/reset-password [post]
+func (h *UserHandler) ResetUserPassword(c *gin.Context) {
+	id := c.Param("id")
+
+	var req services.ResetPasswordRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "invalid request",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	err := h.userService.ResetUserPassword(c.Request.Context(), id, &req)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{
+			Error:   "failed to reset password",
+			Message: err.Error(),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, SuccessResponse{
+		Message: "password reset successfully",
+	})
+}