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>

src/voxip_kiosk/agent.py

@@ -46,7 +46,7 @@ BLANK_URLS = {"", "about:blank", "chrome://newtab/", "chrome://new-tab-page/"}
 
 def probe(url: str, timeout: float = 8.0) -> tuple[bool, str]:
     """Is ``url`` reachable over HTTPS with a valid certificate? → (ok, reason)."""
-    req = urllib.request.Request(url, method="HEAD", headers={"User-Agent": "VoxIP-Kiosk-OS/agent"})
+    req = urllib.request.Request(url, method="HEAD", headers={"User-Agent": "Daynivo-Kiosk-OS/agent"})
     try:
         with urllib.request.urlopen(req, timeout=timeout, context=ssl.create_default_context()):
             return True, ""