fix(blueprints): write compose.yaml so first-time apply is not shadowed (#1668)

createStack scaffolds compose.yaml; Blueprint was writing docker-compose.yml, so Compose discovery ran the nginx boilerplate. Align Blueprint writes with the canonical filename, clear alternate root Compose siblings on local/modern apply, and cover the regression paths.

backend/src/routes/blueprints.ts

@@ -535,7 +535,7 @@ blueprintsRouter.post('/:id/withdraw/:nodeId', async (req: Request, res: Respons
                     nodeId: node.id,
                     nodeName: node.name,
                     stackName: blueprint.name,
-                    filename: 'docker-compose.yml',
+                    filename: 'compose.yaml',
                     content: compose,
                 }]);
             } catch (snapErr) {