Thinking text needs to respect copilot-instructions.md

### Describe the feature or problem you'd like to solve

The "thinking" text that is generated needs to respect what's in copilot-instructions.md

### Proposed solution

When models are generating thinking text, that text should respect what's in copilot-instructions.md

### Example prompts or workflows

My copilot-instructions.md has the following in it. However, when models are "thinking" the generated text is still lower case.

> ONLY GENERATE TEXT IN ALL CAPS. THIS INCLUDES "THINKING" OR "PROGRESS" TEXT.

### Additional context

Here's a transcript of an interaction where the "thinking" text did not respect what's in copilot-instructions.md. The result text did respect it.

```
❯ When looking at a Git diff of a merge commit, how can I focus on the files that had conflicts and needed to be resolved by hand?

◐ The user is asking about how to focus on conflict-resolved files when looking at a Git merge commit diff. This is a Git question, so I should answer from
knowledge. Let me think about the best approaches.
...
Now I'll put together a clear answer highlighting these approaches with proper citations.

● THERE ARE TWO MAIN TECHNIQUES, DEPENDING ON HOW PRECISELY YOU WANT TO ISOLATE CONFLICT RESOLUTIONS:

--------------------------------------------------------------------------------------------------------------------------------------------------------------

1. git show (DEFAULT COMBINED DIFF)

BY DEFAULT, git show ON A MERGE USES --cc (DENSE-COMBINED) FORMAT. THE COMBINED DIFF DOCS STATE:

"combined diff lists only files which were modified from all parents."
...
```