ci: add manual desktop test artifact workflow

[StudentWeis]

Motivation

Ropy needs branch-specific packaged binaries for Linux and Windows GUI end-to-end testing before a release tag exists. The current release workflow primarily packages tagged releases, so AgentBay compatibility testing cannot reliably consume an artifact built from an in-review commit.

Proposed Solution

Add a manually triggered GitHub Actions workflow that builds cargo-dist local artifacts for x86_64-unknown-linux-gnu and x86_64-pc-windows-msvc on their native GitHub-hosted runners. Upload each platform archive, its SHA-256 checksum, and the dist manifest as separate workflow artifacts without creating a GitHub Release.

Alternatives Considered

• Compile inside the AgentBay GUI test sandbox. This contaminates the clean runtime image with development dependencies and can mask packaging problems.
• Push prerelease tags. This creates release-side effects for artifacts that are only intended for validation.

Acceptance Criteria

• The workflow can be triggered manually for a selected branch or commit.
• Linux produces ropy-x86_64-unknown-linux-gnu.tar.xz and a SHA-256 checksum.
• Windows produces ropy-x86_64-pc-windows-msvc.zip and a SHA-256 checksum.
• Each platform uploads a separate GitHub Actions artifact including its dist manifest.
• The workflow does not create or modify a GitHub Release.
• Repository precheck passes.

Scope

other / cross-cutting