feat: add stt-ptt package for voice-to-text and text-to-speech

Implements speech-to-text (via whisper-cpp) and text-to-speech (via espeak)
functionality with key bindings. Replaces coreutils with busybox for lighter
dependencies and removes explicit buildInputs since all paths are hardcoded.

modules/home-manager/cli/default.nix

@@ -1,6 +1,7 @@
 # CLI/Terminal-related Home Manager modules
 {
   imports = [
+    ./stt-ptt.nix
     ./zellij-ps.nix
   ];
 }