report a switch name that matches no registration

[loicveyssiere]

Redis accepts any field, so a mistyped switch name was written, reported as applied, and never consulted — indistinguishable from a working pause until someone noticed the flow had never stopped.

App now tells its SwitchBoard which names this process actually checks, and anything else is logged at ERROR. Checked both on set() and on every re-read: set() catches this process's own callers, the re-read catches whatever switches.disable() wrote from outside, which holds a short-lived connection, knows no topology, and so cannot check itself.

Logged rather than raised — a process knows only the names it mounted, and in a split deployment a name may belong to a service running elsewhere. Reported once per name so a 2s refresh cannot turn one typo into a flood.

Also fixes pytest collection: tests/ has no init.py, so pytest put that directory on sys.path instead of the project root and from tests.helpers import ... only resolved under python -m pytest.