refactor(ssh): restructure inventory and modularize helper logic

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.

modules/desktop/options.nix

@@ -1,4 +1,19 @@
-{ ... }: {
+{ lib, ... }: {
+  # Resolve `wisdom*` HM slices for NixOS `extraModules` (`self` is not an HM specialArg).
+  # Slices are gated by `chiasson.home.*.enable`; hosts only flip toggles in `home.nix`.
+  # Lives here (not `modules/lib/`) because `hosts/desktop-home-base.nix` consumes it and
+  # fragment eval order requires the definition to sort before `hosts/`.
+  flake.lib.wisdomCatalogExtraModules =
+    self:
+    let
+      names = lib.sort builtins.lessThan (
+        lib.filter (n: lib.hasPrefix "wisdom" n && n != "wisdom" && n != "wisdomShellBash") (
+          builtins.attrNames self.homeManagerModules
+        )
+      );
+    in
+    map (name: self.homeManagerModules.${name}) names;
+
   flake.nixosModules.desktopOptions =
     { config, options, lib, pkgs, self, inputs, ... }:
     let