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/deep-links.ts

@@ -1,11 +1,11 @@
 import { app } from 'electron';
 import * as path from 'path';
 import { createWindow, getMainWindow } from '../window/create-window';
+import { resolveSecondInstanceAction } from './second-instance.rules';
 
 const CUSTOM_PROTOCOL = 'toju';
 const DEEP_LINK_PREFIX = `${CUSTOM_PROTOCOL}://`;
 const DEV_SINGLE_INSTANCE_EXIT_CODE_ENV = 'METOYOU_SINGLE_INSTANCE_EXIT_CODE';
-const DEV_RELOAD_EXISTING_ARG = '--metoyou-dev-reload-existing';
 
 let pendingDeepLink: string | null = null;
 
@@ -42,6 +42,24 @@ function focusMainWindow(): void {
   mainWindow.focus();
 }
 
+function reloadMainWindow(): void {
+  const mainWindow = getMainWindow();
+
+  if (!mainWindow || mainWindow.isDestroyed()) {
+    void createWindow();
+
+    return;
+  }
+
+  focusMainWindow();
+
+  if (mainWindow.webContents.isLoadingMainFrame()) {
+    return;
+  }
+
+  mainWindow.webContents.reloadIgnoringCache();
+}
+
 function forwardDeepLink(url: string): void {
   const mainWindow = getMainWindow();
 
@@ -96,13 +114,16 @@ export function initializeDeepLinkHandling(): boolean {
   }
 
   app.on('second-instance', (_event, argv) => {
-    if (resolveDevSingleInstanceExitCode() != null && argv.includes(DEV_RELOAD_EXISTING_ARG)) {
-      app.relaunch();
-      app.exit(0);
-      return;
-    }
+    const action = resolveSecondInstanceAction({
+      argv,
+      devSingleInstanceExitCode: resolveDevSingleInstanceExitCode()
+    });
 
-    focusMainWindow();
+    if (action === 'reload-existing') {
+      reloadMainWindow();
+    } else {
+      focusMainWindow();
+    }
 
     const deepLink = extractDeepLink(argv);