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/editors/cursor.nix

@@ -33,7 +33,9 @@
     in
     {
       options.chiasson.home.editors.cursor = {
-        enable = lib.mkEnableOption "Cursor editor from the `cursor` flake input.";
+        enable = lib.mkEnableOption "Cursor editor from the `cursor` flake input." // {
+          default = true;
+        };
         setAsDefaultEditor = lib.mkOption {
           type = lib.types.bool;
           default = true;

modules/wisdom/editors/kate.nix

@@ -6,7 +6,9 @@
       cfg = config.chiasson.home.editors.kate;
     in
     {
-      options.chiasson.home.editors.kate.enable = lib.mkEnableOption "Kate.";
+      options.chiasson.home.editors.kate.enable = lib.mkEnableOption "Kate." // {
+        default = false;
+      };
 
       config = lib.mkIf (root.enable && cfg.enable) {
         home.packages = lib.optional (

modules/wisdom/editors/obsidian.nix

@@ -8,7 +8,9 @@
     {
       options.chiasson.home.editors.obsidian.enable = lib.mkEnableOption ''
         Obsidian (unfree); skipped if unavailable here.
-      '';
+      '' // {
+        default = true;
+      };
 
       config = lib.mkIf (root.enable && cfg.enable) {
         home.packages = lib.optional (