Add EFI Boot Manager Plugin

[f-ever]

Add EFI Boot Manager to Plugin Store

A graphical interface for managing EFI boot entries on Steam Deck. This plugin provides a clean, intuitive way to:

• Reorder boot entries using up/down buttons to change boot priority
• Set next boot target to temporarily boot into a specific OS on next reboot
• View boot information including current boot entry and next boot target
• Multi-language support with automatic Steam language detection (English, 简体中文)

The plugin wraps the efibootmgr command-line tool with a user-friendly interface, showing only SteamOS and Windows entries for simplicity. This is useful for Steam Deck users who dual-boot Windows and want to easily switch between operating systems without using the boot menu.

Screenshots:

Task Checklist

Developer

• I am the original author or an authorized maintainer of this plugin.
• I have abided by the licenses of the libraries I am utilizing, including attaching license notices where appropriate.

Plugin

• I have verified that my plugin works properly on the Stable and Beta update channels of SteamOS.
• I have verified my plugin is unique or provides more/alternative functionality to a plugin already on the store.

Backend

• No: I am using a custom backend other than Python.
• No: I am using a tool or software from a 3rd party FOSS project that does not have it's dependencies statically linked.
• No: I am using a custom binary that has all of it's dependencies statically linked.

Community

• I have tested and left feedback on two other pull requests for new or updating plugins.
• I have commented links to my testing report in this PR.

Testing

• Tested by a third party on SteamOS Stable or Beta update channel.

[github-actions]

Issues Found

• Both testing boxes are present in your description. Please remove one of them per the Markdown comment above the testing section.

Next Steps

1. If we found any issues above, please edit your pull request description to resolve them and leave a comment saying you've done so.
2. For the quickest review, please see the Community section of the pull request template for how you can help other developers.
3. Once your description is correct, a maintainer will review your pull request as soon as possible.

Thank you for your contribution! If you need any help, please reach out on our Discord server. ❤️

[f-ever]

Issues Found

• Both testing boxes are present in your description. Please remove one of them per the Markdown comment above the testing section.

Next Steps

1. If we found any issues above, please edit your pull request description to resolve them and leave a comment saying you've done so.
2. For the quickest review, please see the Community section of the pull request template for how you can help other developers.
3. Once your description is correct, a maintainer will review your pull request as soon as possible.

Thank you for your contribution! If you need any help, please reach out on our Discord server. ❤️

I have removed the commented out testing boxes.

[beebls]

Code LGTM, however I'm going to ask for a second reviewer with more linux/efi specific experience to give it the final ok

[EMERALD0874]

This looks fine to me, as well. Going to approve this for testing but take some more time to review the code and its possible negative impacts before approving for merge.