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/auth/refresh.go

@@ -1,6 +1,7 @@
 package auth
 
 import (
+	"nixcn-cms/exception"
 	"nixcn-cms/pkgs/authtoken"
 	"nixcn-cms/utils"
 
@@ -14,7 +15,14 @@ func Refresh(c *gin.Context) {
 	}
 
 	if err := c.ShouldBindJSON(&req); err != nil {
-		utils.HttpResponse(c, 400, "", "invalid request")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusClient).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthRefreshEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorInvalidInput).
+			Build()
+		utils.HttpResponse(c, 400, errorCode)
 		return
 	}
 
@@ -24,13 +32,27 @@ func Refresh(c *gin.Context) {
 
 	accessToken, err := JwtTool.RefreshAccessToken(req.RefreshToken)
 	if err != nil {
-		utils.HttpResponse(c, 401, "", "invalid refresh token")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusClient).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthRefreshEndpoint).
+			SetType(exception.ErrorTypeSpecific).
+			SetOriginal(exception.AuthRefreshInvalidToken).
+			Build()
+		utils.HttpResponse(c, 401, errorCode)
 		return
 	}
 
 	refreshToken, err := JwtTool.RenewRefreshToken(req.RefreshToken)
 	if err != nil {
-		utils.HttpResponse(c, 500, "", "error renew refresh token")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusServer).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthRefreshEndpoint).
+			SetType(exception.ErrorTypeSpecific).
+			SetOriginal(exception.AuthRefreshRenewFailed).
+			Build()
+		utils.HttpResponse(c, 500, errorCode)
 		return
 	}