feat(remote-control): viewer can control a desktop sharer's screen, with consent (0.1.13/batch70)

Fixes the core "viewer can't control the sharer even on desktop" gap. Three root
causes addressed:
- share.html DISCARDED every input-channel message (onmessage=()=>{}). It now
  parses the viewer's mouse/keyboard events and forwards them to the desktop shell.
- The main desktop app had NO OS injector (it lived only in the separate agent).
  Ported the nut-js injector (agent/input/inject.js) into desktop/input, wired an
  inject IPC + injectInput bridge, HARD-gated behind a consent flag (rcArmed).
- /share runs in an iframe (no direct bridge access) → it postMessages input to
  the top frame (home.html), which relays to the native bridge.

Consent + safety: the sharer sees an Allow/Deny prompt the first time the agent
interacts; while active a persistent "your screen is being controlled — Stop"
banner; instant revoke; auto-release on session end/teardown. Browser sharers stay
view-only (no OS injection possible). nut-js is an optionalDependency (N-API, ABI-
stable across Electron) — degrades to no-op if the native module is unavailable.
Windows-first; maps to the primary display.

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

desktop/package.json

@@ -1,6 +1,6 @@
 {
   "name": "biz-connect-desktop",
-  "version": "0.1.12",
+  "version": "0.1.13",
   "description": "Biz Connect technician desktop client — loads the Connect web UI with native screen capture",
   "author": {
     "name": "BizGaze",
@@ -14,6 +14,9 @@
   "dependencies": {
     "electron-updater": "^6.3.9"
   },
+  "optionalDependencies": {
+    "@nut-tree-fork/nut-js": "^4.2.0"
+  },
   "devDependencies": {
     "electron": "^31.0.0",
     "electron-builder": "^24.13.3"