refactor(errs): migrate from gperr.Error to standard Go error interface

This is a large-scale refactoring across the codebase that replaces the custom
`gperr.Error` type with Go's standard `error` interface. The changes include:

- Replacing `gperr.Error` return types with `error` in function signatures
- Using `errors.New()` and `fmt.Errorf()` instead of `gperr.New()` and `gperr.Errorf()`
- Using `%w` format verb for error wrapping instead of `.With()` method
- Replacing `gperr.Subject()` calls with `gperr.PrependSubject()`
- Converting error logging from `gperr.Log*()` functions to zerolog's `.Err().Msg()` pattern
- Update NewLogger to handle multiline error message
- Updating `goutils` submodule to latest commit

This refactoring aligns with Go idioms and removes the dependency on
custom error handling abstractions in favor of standard library patterns.

internal/auth/oidc.go

@@ -17,7 +17,6 @@ import (
 	"github.com/rs/zerolog/log"
 	"github.com/yusing/godoxy/internal/common"
 	"github.com/yusing/godoxy/internal/utils"
-	gperr "github.com/yusing/goutils/errs"
 	httputils "github.com/yusing/goutils/http"
 	"golang.org/x/oauth2"
 	"golang.org/x/time/rate"
@@ -76,8 +75,8 @@ const (
 var (
 	errMissingIDToken = errors.New("missing id_token field from oauth token")
 
-	ErrMissingOAuthToken = gperr.New("missing oauth token")
-	ErrInvalidOAuthToken = gperr.New("invalid oauth token")
+	ErrMissingOAuthToken = errors.New("missing oauth token")
+	ErrInvalidOAuthToken = errors.New("invalid oauth token")
 )
 
 // generateState generates a random string for OIDC state.