chore: use stdlib uuid package

Go 1.27 ships a uuid package with the same API, dropping the direct
dependency on github.com/google/uuid.

Assisted-by: Claude:Opus 5

services/auth/source/oauth2/init.go

@@ -15,9 +15,9 @@ import (
 	"gitea.dev/modules/optional"
 	"gitea.dev/modules/setting"
 
-	"github.com/google/uuid"
 	"github.com/gorilla/sessions"
 	"github.com/markbates/goth/gothic"
+	"uuid"
 )
 
 var gothRWMutex = sync.RWMutex{}

services/auth/source/pam/source_authenticate.go

@@ -14,7 +14,7 @@ import (
 	"gitea.dev/modules/optional"
 	"gitea.dev/modules/setting"
 
-	"github.com/google/uuid"
+	"uuid"
 )
 
 // Authenticate queries if login/password is valid against the PAM,