ci(workflows): add desktop test artifact builds

[StudentWeis]

Summary

Add a separate, manually triggered GitHub Actions workflow that builds packaged Linux and Windows artifacts for virtual-desktop GUI testing without creating a release or changing the existing CI workflow.

Linked Issue

Closes #161

Changes

• Build x86_64-unknown-linux-gnu on Ubuntu 22.04 and x86_64-pc-windows-msvc on Windows Server 2022 with cargo-dist 0.32.0.
• Verify each cargo-dist SHA-256 checksum before staging the archive.
• Upload per-platform archives, checksums, and the dist manifest with a seven-day retention period.
• Keep the workflow read-only and cancel superseded runs for the same ref.
• Leave the existing pull-request and main-branch CI workflow unchanged.

Testing

• scripts/precheck.sh passes locally
• New / updated tests cover the change — N/A, workflow-only change
• Workflow YAML parses successfully
• Workflow passes actionlint semantic validation
• Commit hooks pass, including YAML validation
• Manual run 30967626564 packages and uploads both Linux and Windows artifacts
• Downloaded archives contain the expected executable and match their published SHA-256 checksums

Self-Check

• PR title follows Conventional Commits
• No hardcoded user-facing strings — no application strings changed
• Errors defined with thiserror (no manual impl Display/Error) — no Rust errors changed
• No unrelated changes mixed in