[Enhancement] Add Android compatibility skills for system, device, and screen-size readiness

## Summary

I would like to propose adding an Android compatibility skill set to this repository.

I have prepared the initial implementation in my fork:

- Fork repository: https://github.com/qkmaosjtu/skills
- Fork branch: `qkmaosjtu/skills:android-compatibility-skills`
- Compare URL: https://github.com/android/skills/compare/main...qkmaosjtu:android-compatibility-skills?expand=1

The proposed contribution adds three focused skills:

- `system-compatibility`: Android platform release compatibility, behavior changes, SDK setup, targetSdk-gated changes, compatibility toggles, and release readiness.
- `device-compatibility`: device, hardware, OEM, peripheral, ABI, low-memory, and Play filtering compatibility.
- `screen-size-compatibility`: screen size, large-screen, foldable, orientation, resizability, aspect ratio, and desktop-style windowing compatibility.

It also adds an initial Android 17/API 37 compatibility reference pack under `system-compatibility`.

## Motivation

First, thank you to the official Android team for building and maintaining Android and for making Android Skills available. Android's open ecosystem is a major strength for developers and users.

At the same time, because Android is open and widely adopted, apps often need to run across a fragmented device landscape. Many manufacturers customize ROM behavior, framework behavior, hardware integration, background behavior, and sometimes API behavior. This is especially visible in markets such as China, where there are many device manufacturers and heavily customized Android distributions.

For this reason, Android compatibility work often needs to cover more than the official platform API level. Developers need a structured way to reason about:

- Android system release behavior changes.
- Device and OEM-specific compatibility risks.
- Screen size, foldable, tablet, desktop-style, and large-screen behavior.

I believe an Android compatibility skill would be valuable for this project because it gives agents a repeatable workflow for compatibility analysis instead of relying on a loose checklist.

## Request

I noticed the README says public contributions are not currently accepted. I attempted to open a PR from my fork, but GitHub returned a `CreatePullRequest` permission error.

Would the project owners be open to one of the following?

1. Temporarily allowing a PR from my fork for review.
2. Inviting `qkmaosjtu` as a collaborator so I can submit the PR properly.
3. Providing the preferred internal process for proposing this compatibility skill set.

I would be happy to revise the implementation to match the repository's preferred structure, naming, authorship, and review expectations.

## Validation already performed

- Ran `quick_validate.py` for `system-compatibility`.
- Ran `quick_validate.py` for `device-compatibility`.
- Ran `quick_validate.py` for `screen-size-compatibility`.
- Checked the staged diff with `git diff --cached --check`.
- Checked for TODO/template leftovers before committing.

Review the proposed implementation in the qkmaosjtu/skills fork on the android-compatibility-skills branch, using the compare URL in the issue. Start by examining the three named skill areas and run the listed quick_validate.py checks and git diff --cached --check. Done means the maintainers have specified an accepted contribution process and the proposed skills match the repository's review expectations.

Written by the indexing model from the issue text.