System prompt contains incorrect instructions

### Describe the bug

The system prompt contains instructions such as

> You can install Linux, Python, JavaScript and Go packages with the `apt`, `pip`, `npm` and `go` commands.

> You can run Python, Node.js and Go code with `python`, `node` and `go`

This instruction causes to cli to e.g. use python in certain scenarios while it is actually not available. These instructions are infrastructure/host depended and might be true for the github cloud environment but not for locally hosted or self hosted systems.

It should be possible to override the system prompt or such instructions should be removed.

### Affected version

_No response_

### Steps to reproduce the behavior

1. have a system without python installed
2. Instruct the agent to edit a yaml file
3. In many cases the agent will try to validate the yaml using python while it is not available.

### Expected behavior

System prompt doesn't contain incorrect or misleading instructions to prevent copilot doing things that are not possible.

### Additional context

_No response_

Start by locating the system prompt text that asserts apt, pip, npm, go, python, node, and Go are available, then reproduce the YAML-editing scenario on a host without Python. Done means the prompt no longer makes host-dependent availability claims, or provides the requested way to override them; the issue does not name a file or test to run.

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