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.
Wires up nvim-dap, nvim-dap-ui and rustaceanvim, enables the
NvChad blink completion lazyspec, activates the treesitter
ensure_installed list and adds DAP/rustaceanvim keymaps.
