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.

agents-docs/HANDOFF.md

@@ -1,10 +1,6 @@
 # Session Handoff
 
-> **New chat:** attach `@agents-docs/HANDOFF.md` (and only files under Changed files). Say: continue from this handoff; do not redo completed work.
->
-> **Agents cannot open a new chat** — overwrite this file, then ask the user to start one.
->
-> **Keep this file tiny:** always **overwrite** the whole file (never append). When the task is finished, **clear** back to `Status: none` and empty sections (see below).
+> **New chat:** attach `@agents-docs/HANDOFF.md`. Say: continue from this handoff; do not redo completed work.
 
 **Status:** none
 
@@ -14,16 +10,12 @@
 
 ## Changed files
 
-## Decisions (this session only)
+## Decisions
 
 ## Failed approaches
 
-## Current issue / blockers
+## Current issue
 
-## Next steps (exact)
+## Next steps
 
-## Commands to continue
-
-## Scope note
-
-Default: `toju-app/` + targeted `electron/` + `.gitea/workflows/`. Out of scope unless listed here: `server/`, `e2e/`, `website/`, `docs-site/`.
+## Commands