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.

electron/app/second-instance.rules.spec.ts

@@ -0,0 +1,44 @@
+import {
+  describe,
+  expect,
+  it
+} from 'vitest';
+
+import { DEV_RELOAD_EXISTING_ARG, resolveSecondInstanceAction } from './second-instance.rules';
+
+describe('resolveSecondInstanceAction', () => {
+  it('reloads the open window when a dev launch asks to reuse it', () => {
+    const action = resolveSecondInstanceAction({
+      argv: [
+        'electron',
+        '.',
+        DEV_RELOAD_EXISTING_ARG
+      ],
+      devSingleInstanceExitCode: 23
+    });
+
+    expect(action).toBe('reload-existing');
+  });
+
+  it('never asks a packaged instance to reload, even with the dev argument', () => {
+    const action = resolveSecondInstanceAction({
+      argv: ['metoyou', DEV_RELOAD_EXISTING_ARG],
+      devSingleInstanceExitCode: null
+    });
+
+    expect(action).toBe('focus');
+  });
+
+  it('focuses the open window for an ordinary second launch', () => {
+    const action = resolveSecondInstanceAction({
+      argv: [
+        'electron',
+        '.',
+        'toju://invite/abc'
+      ],
+      devSingleInstanceExitCode: 23
+    });
+
+    expect(action).toBe('focus');
+  });
+});