refactor(wisdom): decentralize module defaults and update conventions

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

modules/wisdom/apps/discord.nix

@@ -12,7 +12,9 @@
 
       options.chiasson.home.apps.discord.enable = lib.mkEnableOption ''
         Vesktop (nixcord). Needs nixpkgs `discord` — breaks on e.g. aarch64-linux.
-      '';
+      '' // {
+        default = false;
+      };
 
       config = lib.mkIf root.enable (lib.mkMerge [
         {

modules/wisdom/apps/localsend.nix

@@ -29,7 +29,9 @@
       options.chiasson.home.apps.localsend = {
         enable = lib.mkEnableOption ''
           LocalSend client; open the firewall on NixOS with `system.localsend` if you want inbound.
-        '';
+        '' // {
+          default = true;
+        };
 
         package = lib.mkPackageOption pkgs "localsend" { };
       };

modules/wisdom/apps/pokeclicker/default.nix

@@ -7,7 +7,9 @@
       pokeclickerPkg = pkgs.callPackage ./package { };
     in
     {
-      options.chiasson.home.apps.pokeclicker.enable = lib.mkEnableOption "PokéClicker desktop (Farigh fork .deb → nix).";
+      options.chiasson.home.apps.pokeclicker.enable = lib.mkEnableOption "PokéClicker desktop (Farigh fork .deb → nix)." // {
+        default = false;
+      };
 
       config = lib.mkIf (root.enable && cfg.enable) {
         home.packages = [ pokeclickerPkg ];