#3139 serve check-config writes the extension catalog into the repo, though its help says nothing is written

swamp serve check-config says "It reads only this repository's files ... Nothing is written to the repository or the vault." In a freshly initialized repo, its first run creates .swamp/_extension_catalog.db, -shm and -wal.

Repro: swamp init swamp serve check-config --auth-mode none ls .swamp # _extension_catalog.db, _extension_catalog.db-shm, _extension_catalog.db-wal

Seen on 20261006.231101.0 (stable) and on the swamp-club#3129 branch. Other repo commands (data query, model type search) create the catalog the same way on first use, so it looks like CLI startup opens or creates the catalog for every command, check-config included.

Expected: check-config leaves the repository untouched, as its help text says, or the help text says the catalog may be created.

The swamp-uat test "swamp serve check-config reports restriction entries offline and without writing to the repo" (tests/cli/serve/none/check_config_test.ts, swamp-uat#564) runs check-config once before comparing the repo, to work around this; drop that step once this is fixed.