Fix empty Bluetooth lists in web mixer; advertise it over Bonjour

busctl cannot convert some BlueZ advertisement data (Apple
ManufacturerData, a{qv}) to JSON, so GetManagedObjects failed as soon as
an iPad was paired and the web showed no devices at all. Read only the
needed Device1/Adapter1 properties per object instead. Also publish the
web mixer as an _http._tcp Avahi service.

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

scripts/install-web.sh

@@ -22,6 +22,20 @@ NoNewPrivileges=true
 [Install]
 WantedBy=multi-user.target
 UNIT
+# Advertise the web mixer over Bonjour/mDNS (_http._tcp) next to HOSTNAME.local.
+install -d -m 755 /etc/avahi/services
+cat > /etc/avahi/services/radxa-mixer.service <<'AVAHI'
+<?xml version="1.0" standalone='no'?>
+<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
+<service-group>
+  <name replace-wildcards="yes">Radxa Mixer (%h)</name>
+  <service>
+    <type>_http._tcp</type>
+    <port>80</port>
+    <txt-record>path=/</txt-record>
+  </service>
+</service-group>
+AVAHI
 systemctl daemon-reload
 systemctl enable --now radxa-mixer-web
 systemctl restart radxa-mixer-web