Add GitHub Actions build and test workflow

[brndnsvr]

Summary

• add a GitHub Actions workflow that builds the VirtualBuddy host app, guest app, and vctool
• run the existing VirtualWormhole test suite on an ARM macOS runner
• make the packet encoding test independent of unspecified JSON object key ordering

Why

The repository currently has no automated build or test gate. This adds a focused CI check for the shipping products and existing tests without requiring signing credentials or persistent artifacts.

The existing packet encoding assertion compared the entire JSON payload byte-for-byte. JSON object key ordering is not guaranteed and differs between toolchains, so the test now keeps the binary packet header assertion exact while comparing the decoded payload semantically.

Validation

• built VirtualBuddy, VirtualBuddyGuest, and vctool locally with Xcode 27 and code signing disabled
• ran all VirtualWormhole tests locally
• passed a fork branch-push workflow run: https://github.com/brndnsvr/VirtualBuddy/actions/runs/29193208621
• passed fork pull-request workflow runs, including the final upstream-ready workflow: https://github.com/brndnsvr/VirtualBuddy/actions/runs/29193420584

[insidegui]

Thank you for the contribution, but I already have an internal CI setup via Xcode Cloud, and in general I do not accept pull requests that change project infrastructure.