Rename musikserverwohnzimmeroben -> musicdolphin

The Pi's OS hostname was changed first (raspi-config do_hostname +
reboot), since no mediapi sets ansible_host and Ansible resolves these
by hostname via mDNS/router DNS. Host now answers as musicdolphin.local
at 192.168.178.100.

The motd file must match the live OS hostname (pi_standard_setup reads
it off the device), the host_vars filename and the pi_musicmouse config
filename must match the inventory key.

sensor_room_name/sensor_room_name_ascii stay WohnzimmerOben - they name
the physical room for MQTT topics, not the host, and renaming them would
orphan the Home Assistant history.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

working.yml

@@ -4,8 +4,8 @@
   roles:
     - bluetooth_monitor
 
-- name: Musikserver Wohnzimmer oben
-  hosts: musikserverwohnzimmeroben
+- name: MusicDolphin oben
+  hosts: musicdolphin
   roles:
     - bluetooth_monitor