feat(stt): add local speech-to-text with whisper.cpp

- Add stt-dictate script for push-to-talk dictation
- Add Mod+Space keybinding in i3 (hold to record, release to transcribe)
- Add whisper-cpp, alsa-utils, xdotool, libnotify packages
- Enable dunst notification daemon

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

home.nix

@@ -8,6 +8,10 @@
 
   home.file.".config/traefik/traefik.toml".source = ./files/traefik.toml;
   home.file.".npmrc".source = ./files/.npmrc;
+  home.file.".local/bin/stt-dictate" = {
+    source = ./files/stt-dictate.sh;
+    executable = true;
+  };
 
   imports =
     [
@@ -49,6 +53,7 @@
 
   services.unclutter.enable = true;
   services.blueman-applet.enable = true;
+  services.dunst.enable = true;  # notification daemon
 
   services.udiskie.enable = true; # require "services.udisks2.enable = true" in system configuration
 }