Feature Request: Add :Copilot Ask FastCommand for Quick Inline Queries

I’ve noticed that the Copilot Chat feature is still being explored ([here](https://github.com/github/copilot.vim/issues/57))

In the meantime, I would like to propose a lightweight feature that could provide immediate value: a "FastCommand"` interface for quick, inline queries.

Proposed Feature:

Introduce a command such as: `:Copilot Ask center the div`

This command would send the prompt directly to Copilot and apply the result to the current file buffer (or return an inline suggestion), without requiring a full chat interface.

先閱讀 issue #57 中連結的 Copilot Chat 討論，然後釐清提議的 :Copilot Ask 命令應如何處理 prompts、傳回的結果、緩衝區變更和內嵌建議。未指定檔案、測試或實作進入點；done 應包含已達成共識的命令行為和相應的驗證。

由索引模型根據 Issue 內容生成。