CloudQueryError prevents /chronicle standup despite local fallback data

### Describe the bug

## Summary

`/chronicle standup` fails when the cloud session store returns `CloudQueryError: internal server error`.

Local session data is available, and some `session_store_sql` queries successfully return local fallback rows. However, the DuckDB-style timestamp predicates used for last-24-hours chronicle queries appear to prevent local fallback from rescuing the command.

## Environment

- GitHub Copilot CLI: `1.0.64`
- Platform: Windows
- Package metadata: `@github/copilot` `1.0.64`, build metadata `ae586e7`
- Startup log showed: `No update needed, current version is 1.0.64, fetched latest release is v1.0.64`

## Impact

`/chronicle standup` cannot generate a standup report even though recent local session rows are available.

## Expected behavior

When the cloud session store fails with an internal server error, `session_store_sql` and `/chronicle standup` should degrade gracefully to local indexed sessions where possible, returning local rows with a warning.

## Actual behavior

The required last-24-hours query fails with:

```text
CloudQueryError: {"documentation_url":"https://docs.github.com/rest","message":"internal server error"}
```

### Affected version

1.0.64

### Steps to reproduce the behavior

This query fails completely:

SELECT id, branch, updated_at
FROM sessions
WHERE updated_at >= TIMESTAMP '2026-06-23T07:47:34.106Z'
ORDER BY updated_at DESC
LIMIT 5

This also failed:

SELECT id, branch, updated_at
FROM sessions
WHERE updated_at >= now() - INTERVAL '1 day'
ORDER BY updated_at DESC
LIMIT 5

But this query returns local fallback rows:

SELECT id, branch, updated_at
FROM sessions
ORDER BY updated_at DESC
LIMIT 5

Observed fallback behavior:

5 row(s) returned from _query_source = local
Cloud query failed (CloudQueryError: {"documentation_url":"https://docs.github.com/rest","message":"internal server error"}). Showing local results only.

### Expected behavior

_No response_

### Additional context

_No response_

从 session_store_sql 的处理和 /chronicle standup 查询路径开始。重现按时间戳筛选的查询，并将其与未筛选的本地回退查询进行比较；当 cloud 查询失败时，/chronicle standup 能够在发出警告的同时返回本地索引的会话，即表示完成。

由索引模型根据 Issue 内容生成。