Move Home Manager module defaults from a centralized `desktop-home-defaults.nix`
file into their respective `wisdom` slices. This change aligns with the
updated documentation regarding module ownership, where defaults live
with the option that owns them rather than in a shared defaults file.
Additionally, update `docs/conventions.md` to reflect this new pattern for
defining `mkEnableOption` defaults and move base git/encryption
configurations into the core `wisdom` module.
- Delete `modules/hosts/desktop-home-defaults.nix`
- Update `modules/wisdom/default.nix` to include shared git and package defaults
- Add `default = ...` to `mkEnableOption` in various `wisdom` modules
- Update `docs/conventions.md` with new HM slice guidelines
Relocate SSH inventory and rbw socket wiring from `modules/lib/` to
dedicated `modules/ssh/` modules to improve logical grouping.
- Move `ssh-inventory.nix` to `modules/ssh/inventory.nix`.
- Move `rbw-ssh-socket.nix` to `modules/ssh/rbw.nix`.
- Relocate `users-merge.nix` logic into `modules/system/users.nix` to
reduce dependency on generic library modules.
- Update `docs/conventions.md` to reflect new module paths.
- Refactor `modules/deploy/navi.nix` to use a local helper for
generating Navi hive configurations.
- Add Pi5 specific Niri KDL configuration snippets.
Olivier