feat(triggershell): add Spotify stop playback command

Pauses Spotify via its MPRIS D-Bus interface. Talks to the user bus
socket directly ($XDG_RUNTIME_DIR/bus) since triggershell.service starts
before the graphical session and lacks DBUS_SESSION_BUS_ADDRESS. No-op
when Spotify is not running.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016uCHmJ3PGcHZGtx8mYqmQG

triggershell.yml

@@ -378,6 +378,33 @@ scripts:
     timeoutSeconds: 20
     variables: []
 
+  - id: spotify-stop
+    name: "Spotify: Stop Playback"
+    description: >-
+      Pauses Spotify playback on the local session via its MPRIS D-Bus
+      interface. Does nothing if Spotify is not running.
+    command: bash
+    args:
+      - -c
+      - |
+        # triggershell.service starts before the graphical session and has no
+        # DBUS_SESSION_BUS_ADDRESS, so point dbus-send at the user bus socket
+        # directly (systemctl --user works here, so this socket exists).
+        bus="unix:path=${XDG_RUNTIME_DIR:-/run/user/$(id -u)}/bus"
+        if ! dbus-send --bus="$bus" --print-reply --dest=org.freedesktop.DBus \
+            /org/freedesktop/DBus org.freedesktop.DBus.ListNames 2>/dev/null \
+            | grep -q '"org.mpris.MediaPlayer2.spotify"'; then
+          echo "Spotify is not running."
+          exit 0
+        fi
+        exec dbus-send --bus="$bus" --print-reply --type=method_call \
+          --dest=org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 \
+          org.mpris.MediaPlayer2.Player.Pause
+      - spotify-stop
+    cwd: ./
+    timeoutSeconds: 15
+    variables: []
+
   - id: system-shutdown
     name: "System: Shutdown"
     description: >-