Prefork worker consolidation (decnet.prefork + decnet fleet heavy),
ATT&CK 19.1 relocation to decnet/data/, and removal of the 10 per-worker
unit templates superseded by the supervisor groups + heavy fleet.
Bundle pointer moved from repo root to decnet/data/ (with LICENSE.txt),
gitignored + fetched on demand (51MB, MITRE-licensed). Version pin bumped
19.0->19.1 with the new sha256; license unchanged. All _REPO_BUNDLE test
constants repointed. Fixes test-web failures after the repo-root bundle
was deleted.