Add Release Deck plugin

[RhanCandia]

Add Release Deck to Plugin Store

Release Deck is a package manager and GitHub release downloader built specifically for SteamOS Gaming Mode in the Quick Access Menu (... button).

What Release Deck Does:

• Discover & Download: Browse tracked GitHub repositories, drill down into releases/tags, read interactive changelogs, and download game ports, AppImages, and standalone packages directly without entering Desktop Mode.
• Smart SteamOS Compatibility: Highlights Linux compatible packages (.AppImage, .tar.gz, x86_64) with badges, while also supporting Windows .exe standalone packages for Proton.
• Non-Steam Shortcut Integration: 1-click adds installed applications and games directly to your Steam Library with clean app naming.
• Installed App Management: Collapsible card layout, automatic executable detection and selector, in-place version update checks, and safe uninstallation.
• Live Background Downloader: Non-blocking downloads with live speed (MB/s), byte counter, and progress bar.

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.
• Generative AI was NOT used to write a majority of the code I am submitting.

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.

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