IDE auto-connect falsely skipped as "already in use by another client" after forking/closing a session

### Describe the bug

After forking a session and later closing that fork, restarting/resuming the original session logs:

```
IDE auto-connect skipped: session is already in use by another client
```

and the CLI does **not** auto-connect to the IDE — even though no other client or session is actually running.

**Root cause (from the shipped bundle, v1.0.68):**

- On create/resume, `alreadyInUse = registerSessionLock(sessionId, dir)`, which returns `aliveCount > 0` from an in-use lock **sweep** — i.e. whether any *other* live lock holder exists for that `sessionId`.
- Lock liveness is tested with **`process.kill(pid, 0)` only** — host-local PID, with no hostname / boot-id / process-start-time recorded. The lock is keyed by `sessionId` and stores a per-PID file.
- If the previous run of the session exited abruptly (crash, kill, or the fork-close workflow) it leaves a **stale in-use lock file**. On restart the recorded PID is either still alive or has been **reused** by an unrelated process, so the sweep counts it as alive → false `alreadyInUse = true`.
- This is aggravated on shared/NFS state directories, where a PID from a *different host* passes the local `kill(pid, 0)` check.

Impact is low/cosmetic-functional: IDE auto-connect is suppressed for that session (no editor attach); it is logged ephemerally + a telemetry event. Core CLI behavior is otherwise unaffected.

### Affected version

GitHub Copilot CLI 1.0.68

### Steps to reproduce the behavior

1. Start a session (S).
2. Fork S into a separate session, open it, do some work, then close it.
3. Restart / resume the original session S.
4. Observe the log line `IDE auto-connect skipped: session is already in use by another client`, and that the IDE is not auto-connected — despite no other client running.

### Expected behavior

When a session is restarted/resumed and no live client actually holds it, the CLI should detect the session as free and auto-connect to the IDE normally, as on a first launch.

Specifically:
- A stale in-use lock left by a previously-exited (crashed, killed, or abruptly-closed) client — including one left by the fork workflow — must **not** be counted as a live holder.
- Lock liveness must be immune to PID reuse, and a lock from a different host (shared/NFS state) must not be treated as locally "alive".
- The `session is already in use by another client` message should appear **only** when a genuinely running, live client on the same host currently owns that session.

### Additional context

Suggested fix: record `{pid, hostname, boot-id or process start-time}` in the in-use lock file and count it alive only when all match (skip locks from other hosts); and reliably release the in-use lock on session close / fork-close.

Start at registerSessionLock(sessionId, dir) and the process.kill(pid, 0) liveness check in the shipped bundle, then trace the create/resume and fork-close paths. Confirm how stale lock files survive abrupt exits and shared state directories. Done means only a genuinely live client on the same host blocks IDE auto-connect, while stale, reused-PID, and foreign-host locks do not.

Rédigé par le modèle d'indexation à partir du texte de l'issue.