feat(talk): support stdin piping

Argument has priority, otherwise read from stdin when piped.
Enables: echo 'Build fertig' | talk
         nixos-rebuild build 2>&1 | tail -3 | talk

pkgs/talk/default.nix

@@ -20,7 +20,15 @@
     # ── Config ──────────────────────────────────────────────────────
     API_KEY="''${ELEVENLABS_API_KEY:?Set ELEVENLABS_API_KEY in your environment}"
     VOICE_ID="''${ELEVENLABS_VOICE_ID:-KXxZd16DiBqt82nbarJx}"
-    TEXT="''${1:?Usage: talk \"Text zum Sprechen\"}"
+    # Argument hat Vorrang, sonst stdin lesen wenn Pipe
+    if [ $# -ge 1 ]; then
+      TEXT="$1"
+    elif [ ! -t 0 ]; then
+      TEXT=$(cat)
+    else
+      echo "Usage: talk \"Text\"  oder  echo Text | talk" >&2
+      exit 1
+    fi
     AUDIO_FILE="/tmp/voice-notify-$$.mp3"
     ACTION_FILE="/tmp/voice-action-$$"