Conflicts:
- `app/helpers/theme_helper.rb`:
Upstream added fallback behavior for when the admin-set theme does not exist.
Glitch-soc has a different theming system, but already had similar fallback,
so not changing glitch-soc code.
- `spec/helpers/theme_helper_spec.rb`:
Upstream adapted existing tests for the new fallback behavior, and added some
tests accordingly.
Glitch-soc has a different theming system, adapted the new tests accordingly.
e7ee3a997c