Resolves conflict with upstream tmux/blender additions (already covered
by the per-program restructure). Adds weekly nix GC (--delete-older-than 7d),
store auto-optimise, and project CLAUDE.md.
Replaces the monolithic packages-marvin.nix with one file per program
so hosts can opt in selectively. Adds docker, clamav, steam, and
audio keybindings for hivebrain. Fixes monitor order and switches
volume widget to PulseVolume.
