feat: manage Handy preferences and startup declaratively

modules/capabilities/niri/_bindings.nix

@@ -36,7 +36,7 @@ in
   };
 
   # Dictation
-  "Mod+D" = {
+  "Mod+Shift+D" = {
     spawn = [
       handy
       "--toggle-transcription"
@@ -44,7 +44,7 @@ in
     _props.repeat = false;
     _props.hotkey-overlay-title = "Toggle Dictation";
   };
-  "Mod+Shift+D" = {
+  "Mod+Ctrl+D" = {
     spawn = [
       handy
       "--cancel"