destroySession can race with concurrent getOrCreateSession during child-exit await

[fitz123]

Problem

SessionManager.destroySession() closes the child process and deletes the stored session state. During the await this.closeSession(chatId) window (waiting for the child to exit), a concurrent getOrCreateSession call for the same chat can see the still-persisted session in the store, load it, and pass --resume to a new subprocess — effectively resurrecting a session that was supposed to be destroyed.

Current upstream code (bot/src/session-manager.ts)

async destroySession(chatId: string): Promise<void> {
  await this.closeSession(chatId);           // awaits child exit
  this.store.deleteSession(chatId);          // store still has the session until here
  try { cleanupSessionMediaDir(chatId); } catch { /* ignore */ }
}

Race window: between entering closeSession and deleteSession running. closeSession itself persists the final state to the store near its start (`this.store.setSession(chatId, ...)`) before awaiting the child exit. So during the await, the store has a fresh, resumable snapshot and getOrCreateSession will happily resume from it.

Fix (already running in a private workspace fork)

1. Delete store entry FIRST so concurrent lookups miss.
2. Call closeSession with { persist: false } so it does not re-persist the final state on the way out.

```ts
async closeSession(chatId: string, { persist = true }: { persist?: boolean } = {}): Promise {
// ...
if (persist) {
this.store.setSession(chatId, this.toSessionState(chatId, session));
}
// ...
}

async destroySession(chatId: string): Promise {
this.store.deleteSession(chatId);
await this.closeSession(chatId, { persist: false });
try { cleanupSessionMediaDir(chatId); } catch { /* ignore */ }
}
```

Evidence: this change has been running in a private workspace fork since 2026-04-02 (commit 2964298) with no observed resurrection regressions, and was the resolution picked during the PR #104 merge conflict.

Acceptance

• destroySession removes store entry before awaiting child exit
• closeSession accepts { persist?: boolean } option (default true)
• Unit test: concurrent destroySession + getOrCreateSession on same chatId — new session must not see resumed state
• Existing media cleanup on destroy is preserved