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.

e2e/helpers/start-test-server.js

@@ -22,7 +22,11 @@ const SERVER_ENTRY = existsSync(SERVER_DIST_ENTRY) ? SERVER_DIST_ENTRY : SERVER_
 const USE_COMPILED_SERVER = SERVER_ENTRY === SERVER_DIST_ENTRY;
 
 // ── Create isolated temp data directory ──────────────────────────────
-const tmpDir = mkdtempSync(join(tmpdir(), 'metoyou-e2e-'));
+// The Playwright helper supplies a durable directory when a test needs to
+// restart the signaling process on the same port without losing its database.
+const suppliedTmpDir = process.env.TEST_SERVER_DATA_DIR;
+const ownsTmpDir = !suppliedTmpDir;
+const tmpDir = suppliedTmpDir || mkdtempSync(join(tmpdir(), 'metoyou-e2e-'));
 const dataDir = join(tmpDir, 'data');
 mkdirSync(dataDir, { recursive: true });
 
@@ -81,6 +85,10 @@ child.on('exit', (code) => {
 
 // ── Cleanup on signals ───────────────────────────────────────────────
 function cleanup() {
+  if (!ownsTmpDir) {
+    return;
+  }
+
   try {
     rmSync(tmpDir, { recursive: true, force: true });
     console.log(`[E2E Server] Cleaned up temp dir: ${tmpDir}`);