chore: dev-stack switches, shared e2e harness, and desktop shell rules

- `LIVE_RELOAD=false npm run dev` keeps the renderer alive across a machine
  suspend; the reload client otherwise destroys the session under test.
- `dev-peer.sh` plus a separate userdata dir runs a second local peer.
- `tools/voice-probe.js` samples peer state and RTP counters from a live
  window, persisting to localStorage so a renderer reload cannot erase it.
- e2e helpers for voice pairs, peer-role election, and a TURN relay.
- Electron single-instance and dev-client-load decisions move into rules
  files with colocated specs.

package.json

@@ -39,6 +39,7 @@
     "build:prod:win": "npm run build:prod:all && electron-builder --win",
     "dev": "npm run build:electron && npm run electron:full",
     "dev:app": "npm run electron:dev",
+    "dev:peer": "./dev-peer.sh",
     "lint": "eslint .",
     "lint:fix": "npm run format && npm run sort:props && eslint . --fix",
     "format": "prettier --write \"toju-app/src/app/**/*.html\"",