Web UI: hide the VLAN split option until it is implemented

The firmware doesn't apply the VLAN split yet (phase 2). The checkbox is
hidden, which also keeps the internet-interface fields and "Web UI / API on"
hidden; the markup stays for phase 2.

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

web/index.html

@@ -147,7 +147,8 @@ e.g. curl -X POST http://p4-aes67.local/api/player/next
 
 <fieldset><legend>Network</legend>
 <label><span>Hostname</span><input name="net.hostname"></label>
-<label><span>VLAN split</span><input name="net.vlan" type="checkbox">
+<!-- VLAN split: not implemented yet (phase 2); hidden until the firmware applies it. -->
+<label hidden><span>VLAN split</span><input name="net.vlan" type="checkbox">
   <small>off: one untagged interface for everything</small></label>
 <p id="netlbl" hidden><b>AES67 interface (untagged)</b></p>
 <label><span>DHCP</span><input name="net.dhcp" type="checkbox"></label>