fix(webrtc): use TURN on desktop too (screen share blank/disconnect)

TURN relay candidates were applied only when IS_MOBILE, leaving desktop
clients STUN-only. Customers behind symmetric NAT / corporate firewalls /
VPNs then couldn't establish the peer connection -> connectionState 'failed'
-> "connection lost" -> blank screen right after granting permissions. This
hit only some users (those needing a relay).

Apply the /api/ice config (STUN + managed TURN) regardless of device, in both
the customer (share.html) and agent (connect.html) flows. Requires TURN_URLS /
TURN_USERNAME / TURN_CREDENTIAL to be set in the production environment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/public/connect.html

 <script>
 let ICE={iceServers:[{urls:'stun:stun.l.google.com:19302'}]};
 const IS_MOBILE=/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini|Mobile/i.test(navigator.userAgent||'');
-let __icePromise=Promise.resolve();try{__icePromise=fetch('/api/ice').then(r=>r.ok?r.json():null).then(c=>{if(c&&c.iceServers&&IS_MOBILE)ICE=c;}).catch(()=>{});}catch(_){}
+let __icePromise=Promise.resolve();try{__icePromise=fetch('/api/ice').then(r=>r.ok?r.json():null).then(c=>{if(c&&c.iceServers)ICE=c;}).catch(()=>{});}catch(_){}
 async function ensureIce(){try{await __icePromise;}catch(_){}return ICE;}
 function pEsc(s){return String(s==null?'':s).replace(/[&<>"]/g,c=>({'&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;'}[c]));}
 // When embedded in the home shell, tell the parent when a session is live so the

server/public/share.html

 let SHARER_NAME='Customer';
 try{fetch('/api/me').then(r=>r.ok?r.json():null).then(m=>{if(m&&(m.name||m.email))SHARER_NAME=m.name||m.email;}).catch(()=>{});}catch(_){}
 const IS_MOBILE=/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini|Mobile/i.test(navigator.userAgent||'');
-let __icePromise=Promise.resolve();try{__icePromise=fetch('/api/ice').then(r=>r.ok?r.json():null).then(c=>{if(c&&c.iceServers&&IS_MOBILE)ICE=c;}).catch(()=>{});}catch(_){}
+let __icePromise=Promise.resolve();try{__icePromise=fetch('/api/ice').then(r=>r.ok?r.json():null).then(c=>{if(c&&c.iceServers)ICE=c;}).catch(()=>{});}catch(_){}
 async function ensureIce(){try{await __icePromise;}catch(_){}return ICE;}
 function pEsc(s){return String(s==null?'':s).replace(/[&<>"]/g,c=>({'&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;'}[c]));}
 // When embedded in the home shell, tell the parent when a session is live so the