deleted sessions still in /chronicle insights

### Describe the bug

I'm following the steps documented [here](https://docs.github.com/en/copilot/concepts/agents/copilot-cli/chronicle#how-session-data-is-stored) to erase my Copilot CLI session history and get back to a pristine state.

After wiping `~/.copilot/session-*`, deleting all synced sessions from GitHub and reindexing, `/chronicle cost-tips` still pulls insights from the deleted sessions. And it is not the only subcommand that exhibits this behavior.

I've inspected the local Sqlite3 database (`~/.copilot/session-store.db`) and the `sessions` table still contained the deleted sessions (they are 11 days old as of today) after it was recreated.

I've tried to turn off the remote session sync features from both my organization's profile policies and from the Copilot CLI settings (`remoteExport` and `remoteSessions`) ― the deleted sessions are still in `/chronicle` insights!

I'm trying to get back to a pristine state because cost tips and other insights I'm getting relate to outdated habits and don't reflect the current ones.

### Affected version

GitHub Copilot CLI 1.0.62

### Steps to reproduce the behavior

The steps require a profile with remote session sync enabled and with some session data recorded within the past 1-2 weeks (I'm providing those numbers because they match my scenario).

1. Erase Copilot session data as documented [here](https://docs.github.com/en/copilot/concepts/agents/copilot-cli/chronicle#how-session-data-is-stored) ― Run both local and remote cleanup
2. Run a `/chronicle` query against one of the deleted sessions, i.e. `/chronicle search Some cool session`

### Expected behavior

`/chronicle` should not include deleted sessions in the computed insights.

### Additional context

- Operating system: Ubuntu Server 24.04.4 LTS
- CPU architecture: x86_64
- Terminal emulator: tmux 3.4
- Shell: Bash 5.2.21

Beginne damit, die Bereinigungs- und Abfrageschritte für `/chronicle` zu reproduzieren, und untersuche anschließend `~/.copilot/session-store.db`, insbesondere die Tabelle `sessions`, jeweils vor und nach der Neuindizierung. Verfolge, wie `/chronicle search` und `/chronicle cost-tips` Sitzungsdaten lesen; abgeschlossen ist die Aufgabe, wenn gelöschte Sitzungen nach der lokalen und der entfernten Bereinigung nicht mehr in den berechneten Erkenntnissen erscheinen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.