Jorijn: "all lenses off by default and opt in only". Config::Defaults()
gives every lens run: false; a config that turns on none - a missing
`lenses` key included - has the one problem that names the lenses, so
config, freeze and run all stop on it; the template ships every lens off,
init says to turn lenses on, and the "no lens runs" preflight names the
cause. A consumer config without a `lenses` key now needs one, as the CI
smoke test's does.
Proven with the lens commit before it: the suite (26 passed), and the
dry-run comparison recorded there.
Jorijn van der Graaf
101471d81a