[IDE] Add shortcuts + hints for Duo context menu navigation
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# Problem to solve
It's not obvious how to go back or close the Duo context menu using only the keyboard.
See https://gitlab.com/gitlab-org/editor-extensions/meta/-/issues/223 for more details on the problem and user feedback.
## Why it's important
Learning keyboard patterns improves workflow efficiency and will make Duo UX stickier.
## Proposal
See: https://gitlab.com/gitlab-org/gitlab/-/issues/546092 for additional details on backspace behavior in nested categories.
```gherkin
Scenario: Interact with the context menu via keyboard
Given the user has the context menu open
Then show keyboard shortcuts for available actions
```
## Example
| Current | Proposed |
| ------ | ------ |
|  |  |
## Important links
- [Figma](https://www.figma.com/design/py1XaoxXhPpc1jFocBMUnx/%E2%AD%90-Duo-in-the-IDE--16983?node-id=3581-8990&t=qlJE8xkWORZTMdcK-1)
- [Prototype iteration 3](https://prototyping-939024.gitlab.io/) (to illustrate the concept, not a 1:1 spec)
issue