refactor: standardize error handling with exception.Builder

- Replace hardcoded error messages with structured error codes using exception.Builder.
- Introduce new common error constants in exception/common.go (CommonErrorInvalidInput, CommonErrorUserNotFound, etc.).
- Update exception/specific.go with domain-specific errors and remove redundant ones.
- Apply consistent error handling across auth, event, user services and middleware.

Co-authored-by: Gemini <gemini@google.com>
Signed-off-by: Noa Virellia <noa@requiem.garden>

service/user/info.go

@@ -2,6 +2,7 @@ package user
 
 import (
 	"nixcn-cms/data"
+	"nixcn-cms/exception"
 	"nixcn-cms/utils"
 
 	"github.com/gin-gonic/gin"
@@ -12,19 +13,40 @@ func Info(c *gin.Context) {
 	userData := new(data.User)
 	userIdOrig, ok := c.Get("user_id")
 	if !ok {
-		utils.HttpResponse(c, 403, "", "userid error")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusUser).
+			SetService(exception.UserService).
+			SetEndpoint(exception.UserInfoEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorMissingUserId).
+			Build()
+		utils.HttpResponse(c, 403, errorCode)
 		return
 	}
 	userId, err := uuid.Parse(userIdOrig.(string))
 	if err != nil {
-		utils.HttpResponse(c, 500, "", "failed to parse uuid")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusServer).
+			SetService(exception.UserService).
+			SetEndpoint(exception.UserInfoEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorUuidParseFailed).
+			Build()
+		utils.HttpResponse(c, 500, errorCode)
 		return
 	}
 
 	// Get user from database
 	user, err := userData.GetByUserId(userId)
 	if err != nil {
-		utils.HttpResponse(c, 404, "", "user not found")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusUser).
+			SetService(exception.UserService).
+			SetEndpoint(exception.UserInfoEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorUserNotFound).
+			Build()
+		utils.HttpResponse(c, 404, errorCode)
 		return
 	}