Introduce downlink.py as the single authority for hotspot eligibility (OPTIONS,
slot busy, post-TX GROUP_HANGTIME). send_peer and BRDG fan-out share the same
gate; monitor events carry stream id from BRDG so new QSOs after hangtime
display without replaying calls blocked during the hangtime window.
Planned release: 2.2.0
Normalize all Python sources to the standard ADN copyright block with
complete GPLv3 notice. Add legacy attribution on routing and dmr_utils
ports; drop SemVer wording from changelog and fix an unused test import.
Rodrigo Pérez