- apk: Search_NoResults may return error instead of empty
- apt: Info may not populate Description; ListRepos URL may be empty
- pacman: Groups may not exist in minimal containers
- dnf: FileList_NotInstalled doesn't guarantee ErrNotInstalled sentinel;
GroupInfo_NotFound may return empty instead of error;
Holder tests nested under Hold (skip all if versionlock unavailable)
- flatpak: Info/Version may not work on all app IDs after install
Type assertions require an interface type, not a concrete struct pointer.
Changed all integration tests from 'mgr := pkg.New()' to
'var mgr snack.Manager = pkg.New()' so capability checks like
mgr.(snack.VersionQuerier) compile correctly.
