fix(agent): remote-control input now works (data channel + nut-js API)

Two latent bugs that broke input control on any setup:
- Data channel was created by the viewer (the answerer), so the agent's offer had
  no SCTP m-line and the channel never opened -> no input reached the agent. The
  agent (offerer) now creates the 'input' channel; the viewer receives it.
- inject.js used nut.screen.getResolution() which doesn't exist in this nut-js;
  switched to screen.width()/height() with per-session caching.

Verified end-to-end locally: screen streams + mouse injection moves the remote cursor.
Also commits desktop/ + mobile/ package-lock.json from client installs.

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

agent/renderer/agent.js

@@ -104,13 +104,13 @@ async function startStreaming() {
   pc = new RTCPeerConnection({ iceServers: [{ urls: 'stun:stun.l.google.com:19302' }] });
   localStream.getTracks().forEach((t) => pc.addTrack(t, localStream));
 
-  // Viewer creates the input data channel; we receive it here.
-  pc.ondatachannel = (ev) => {
-    const ch = ev.channel;
-    ch.onmessage = (msg) => {
-      let evt; try { evt = JSON.parse(msg.data); } catch { return; }
-      window.agent.injectInput(evt); // -> main process -> OS injection
-    };
+  // The agent is the OFFERER, so it must create the input data channel — otherwise the
+  // SCTP m-line is absent from the offer and the channel never negotiates (viewer's stays
+  // closed, so no input arrives). The viewer receives this channel via ondatachannel.
+  const inputCh = pc.createDataChannel('input', { ordered: true });
+  inputCh.onmessage = (msg) => {
+    let evt; try { evt = JSON.parse(msg.data); } catch { return; }
+    window.agent.injectInput(evt); // -> main process -> OS injection
   };
 
   pc.onicecandidate = (ev) => {