Whole-branch review found the stamping test was structurally vacuous: a bare
foreach over ChannelTemplates.Where(IsSystem) passes with zero iterations, so
the test would have stayed green if template seeding silently bailed out.
Assert the collection is non-empty first. Proven non-vacuous by a negative
control (forcing SeedChannelTemplates to bail makes exactly this test fail).
Also cover the ACTUAL production sequence -- adopt an existing hand-made row,
then delete it -- which the previous no-resurrect test did not exercise (it
covered seed-then-delete). The marker is written on the adopt path too, so
the deleted row must stay deleted.
docs: note that a deleted preset degrades to no default rather than failing,
and that the default applies to newly created channels, not retroactively.
Refs #67
timothy