refactor: introduce Wire dependency injection and interface-based architecture

- Add Google Wire for compile-time dependency injection
- Replace concrete service types with interfaces across handlers
- Remove global state (DB, cache) in favor of constructor injection
- Split monolithic files into focused modules:
  - config: separate files for each config domain
  - dto: converters split by domain (user, post, message, group)
  - cache: separate metrics.go and redis_cache.go
- Introduce unified apperrors package with string-based error codes
- Add transaction support with context-aware repository methods
- Upgrade golang.org/x/crypto from 0.17.0 to 0.26.0

internal/handler/system_message_handler.go

@@ -4,6 +4,7 @@ import (
 	"strconv"
 
 	"carrot_bbs/internal/cache"
+
 	"github.com/gin-gonic/gin"
 
 	"carrot_bbs/internal/dto"
@@ -16,16 +17,19 @@ import (
 type SystemMessageHandler struct {
 	systemMsgService service.SystemMessageService
 	notifyRepo       *repository.SystemNotificationRepository
+	cache            cache.Cache
 }
 
 // NewSystemMessageHandler 创建系统消息处理器
 func NewSystemMessageHandler(
 	systemMsgService service.SystemMessageService,
 	notifyRepo *repository.SystemNotificationRepository,
+	cacheBackend cache.Cache,
 ) *SystemMessageHandler {
 	return &SystemMessageHandler{
 		systemMsgService: systemMsgService,
 		notifyRepo:       notifyRepo,
+		cache:            cacheBackend,
 	}
 }
 
@@ -101,7 +105,7 @@ func (h *SystemMessageHandler) MarkAsRead(c *gin.Context) {
 		response.InternalServerError(c, "failed to mark as read")
 		return
 	}
-	cache.InvalidateUnreadSystem(cache.GetCache(), userID)
+	cache.InvalidateUnreadSystem(h.cache, userID)
 
 	response.SuccessWithMessage(c, "marked as read", nil)
 }
@@ -121,7 +125,7 @@ func (h *SystemMessageHandler) MarkAllAsRead(c *gin.Context) {
 		response.InternalServerError(c, "failed to mark all as read")
 		return
 	}
-	cache.InvalidateUnreadSystem(cache.GetCache(), userID)
+	cache.InvalidateUnreadSystem(h.cache, userID)
 
 	response.SuccessWithMessage(c, "all messages marked as read", nil)
 }
@@ -148,7 +152,7 @@ func (h *SystemMessageHandler) DeleteSystemMessage(c *gin.Context) {
 		response.InternalServerError(c, "failed to delete notification")
 		return
 	}
-	cache.InvalidateUnreadSystem(cache.GetCache(), userID)
+	cache.InvalidateUnreadSystem(h.cache, userID)
 
 	response.SuccessWithMessage(c, "notification deleted", nil)
 }