Package the native plugin workbench helper

[tcballard]

Summary

Package the Workbench helper needed by omarchy#10027, where plugin development and management becomes a first-party Omarchy Shell capability.

• build omarchy-plugin-workbench from the pinned upstream commit
• install only the helper executable, license, and README
• support both x86_64 and aarch64
• run the locked Rust test suite during check()
• publish through the fast release ring so the core migration can install it on existing systems

The source archive is pinned to 4bdab3c7e477f475766f138f7085c42f03ba5586 with SHA-256 b6123d69e66391f9974151cd1b0c4ae0957560e37b968c6572fa8b224c739bd1.

Test evidence

Passed locally:

• source archive checksum verification
• bash -n PKGBUILD
• metadata JSON validation
• git diff --check
• mechanical open-source PR preflight

A clean makepkg build was not available in this container because its Arch packaging and Rust toolchains are absent. The pinned source commit's own CI and reproducible-runtime checks passed before it was merged.