feat(migrate): containr migrate railway — GraphQL import of services/vars/domains (#51)

--token (or RAILWAY_TOKEN) reads the Railway project via backboard
GraphQL: services resolve to git-repo or image services with command +
replicas, variables and service/custom domains follow. --dry-run prints
the plan; --into targets an existing project. Both account (Bearer) and
project tokens (Project-Access-Token header) work.

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app/backend/internal/cli/root.go

@@ -94,6 +94,7 @@ func init() {
 	rootCmd.AddCommand(commands.BannersCmd)
 	rootCmd.AddCommand(commands.InvitesCmd)
 	rootCmd.AddCommand(commands.UpCmd)
+	rootCmd.AddCommand(commands.MigrateCmd)
 }
 
 func initConfig() {