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.

emergency-fix/e2e-failures/00-summary.md

@@ -0,0 +1,19 @@
+# E2E summary
+
+- Run: 2026-08-12T10:58:08Z → 2026-08-12T11:11:34Z UTC
+- **65 passed / 0 failed / 0 flaky / 0 timeouts**
+- Wall: ~13.4 min
+
+## Errors
+
+None.
+
+## Soft signals (passed but slow)
+
+- 128.2s — `voice/mixed-signal-config-voice.spec.ts` — 8 users with different signal configs can voice, mute, deafen, and chat concurrently
+- 125.1s — `voice/multi-signal-eight-user-voice.spec.ts` — keeps 8 users on 2 signal apis while voice, mute, and deafen stay consistent for 20+ seconds
+- 53.4s — `auth/user-session-data-isolation.spec.ts` — gives a new user a blank slate and restores only that user local data after account switches
+- 33.7s — `chat/chat-message-features.spec.ts` — shows per-server channel lists on first saved-server click
+- 30.3s — `chat/multi-client-chat-sync.spec.ts` — syncs messages between same-user devices and late-joining users after offline gaps
+
+See `README.md` for full duration table.