The headless runner still built an ephemeral DatabaseEngine, an EventBus,
and a TempDir that no command read -- a remnant of the CLI-holds-its-own-store
design that predates the gRPC API. Nothing but two dead_code accessors touched
them, so remove the fields, the accessors, and the now-unreachable RunnerError.
With no store to open, construction is neither fallible nor async, so the
constructors lose their Result and async, and 'ephemeral' no longer describes
them: they are renamed connect/connect_with/connect_with_token_override.
Doc comments that contrasted the daemon's persistent store against 'this
runner's own ephemeral local db' now described a field that does not exist;
they are rewritten to say the CLI keeps no store at all.
james.maes