Rename the visible VoxIP texts to Daynivo

Product name (Daynivo Kiosk OS), default device name, kiosk screens,
service descriptions, installer output and docs. Internal names
(voxip-kiosk-*, /etc/voxip-kiosk, user voxip, VOXIP_* variables) stay.
An update renames a device still called "VoxIP Kiosk" to the new default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/config.default.json

@@ -1,5 +1,5 @@
 {
-  "device_name": "VoxIP Kiosk",
+  "device_name": "Daynivo Kiosk",
   "url": "https://schermen-ijsselflat.voxip.nl",
   "refresh_interval": 0,
   "screen_always_on": true,