Q context can be viewed/edited as a normal file

## Problem

The current Q context is not easy to inspect or edit.

## Expected behavior

Q should provide a `Edit Context` command, which opens the AI context as a normal text file in the IDE. The context is updated, when the user saves the file.

Optional: As a step towards https://github.com/aws/aws-toolkit-vscode/issues/6361 , the file should be stored in a fixed location on the filesystem (perhaps per-workspace). When VSCode restarts, the file is loaded as an initial context.

Related:

- https://github.com/aws/aws-toolkit-vscode/issues/6361
- https://github.com/aws/aws-toolkit-vscode/issues/5969
- https://github.com/aws/aws-toolkit-vscode/issues/6359

Start by tracing the existing Q context handling and command registration in the AWS Toolkit for VS Code. Implement an Edit Context command that opens the context as editable text and applies saved changes; if the optional persistence is included, verify workspace storage and restoration after VS Code restarts.

Written by the indexing model from the issue text.