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/token.go

@@ -2,6 +2,7 @@ package auth
 
 import (
 	"nixcn-cms/data"
+	"nixcn-cms/exception"
 	"nixcn-cms/pkgs/authcode"
 	"nixcn-cms/pkgs/authtoken"
 	"nixcn-cms/utils"
@@ -19,20 +20,41 @@ func Token(c *gin.Context) {
 
 	err := c.ShouldBindJSON(&req)
 	if err != nil {
-		utils.HttpResponse(c, 400, "", "invalid request")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusClient).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthTokenEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorInvalidInput).
+			Build()
+		utils.HttpResponse(c, 400, errorCode)
 		return
 	}
 
 	authCode, ok := authcode.VerifyAuthCode(req.Code)
 	if !ok {
-		utils.HttpResponse(c, 403, "", "invalid or expired token")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusClient).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthTokenEndpoint).
+			SetType(exception.ErrorTypeSpecific).
+			SetOriginal(exception.AuthTokenInvalidToken).
+			Build()
+		utils.HttpResponse(c, 403, errorCode)
 		return
 	}
 
 	userData := new(data.User)
 	user, err := userData.GetByEmail(authCode.Email)
 	if err != nil {
-		utils.HttpResponse(c, 500, "", "internal server error")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusServer).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthTokenEndpoint).
+			SetType(exception.ErrorTypeCommon).
+			SetOriginal(exception.CommonErrorInternal).
+			Build()
+		utils.HttpResponse(c, 500, errorCode)
 		return
 	}
 
@@ -42,7 +64,14 @@ func Token(c *gin.Context) {
 	}
 	accessToken, refreshToken, err := JwtTool.IssueTokens(authCode.ClientId, user.UserId)
 	if err != nil {
-		utils.HttpResponse(c, 500, "", "error generating tokens")
+		errorCode := new(exception.Builder).
+			SetStatus(exception.ErrorStatusServer).
+			SetService(exception.AuthService).
+			SetEndpoint(exception.AuthTokenEndpoint).
+			SetType(exception.ErrorTypeSpecific).
+			SetOriginal(exception.AuthTokenGenFailed).
+			Build()
+		utils.HttpResponse(c, 500, errorCode)
 		return
 	}