Bare `#NNNNN` auto-linkifies against the current repo, breaking cross-repo issue/PR references

### Summary

In the CLI's rendered output, a bare `#NNNNN` is auto-linkified as an issue/PR mention resolved against the **current repository's** remote. When the number actually refers to a *different* repository, this produces an incorrect link.

### Environment

- GitHub Copilot CLI v1.0.64 (Linux)

### Example

While working in repository `owner/repoA`, referring to an upstream pull request from another project as `#205054` renders as a link to `https://github.com/owner/repoA/issues/205054` — a bogus URL (there is no such issue in `repoA`; the real reference is `other-org/other-repo#205054`).

### Expected

One of:
- Don't auto-linkify a bare `#NNNNN` unless it resolves to an existing issue/PR in the current repo, **or**
- Provide a setting to disable issue/PR auto-linkification, **or**
- Only auto-linkify qualified references (`owner/repo#NNNN`).

### Impact

Easy to hit whenever working in one repo (e.g. a fork or mirror) while citing issues/PRs from another (e.g. an upstream project). The generated links are misleading. Minor but common.

### Workarounds

Full URL (`https://github.com/org/repo/pull/NNNN`), a qualified `owner/repo#NNNN`, or wrapping the literal in backticks (`` `#NNNN` ``) so it isn't linkified.

### Note

`#` is documented in the CLI help as "mention issues and pull requests". The request is to make a bare cross-repo number either non-linkified or configurable.

issue 中沒有指定原始檔案或測試。先找出 CLI 對 issue 和 pull request 自動連結的渲染輸出處理，然後重現跨 repository 的範例 `#205054`；當裸引用不再產生指向目前 repository 的誤導性連結，且選定的行為已由測試涵蓋時，即表示完成。

由索引模型根據 Issue 內容生成。