Establish entitlements and signing for running a VM

[ispy4you]

Running a guest needs com.apple.security.virtualization, which means the code has to be built and signed as an app bundle — swift run will not do.

Work out the smallest setup that lets a developer clone the repository and boot a VM locally, and write it down in Docs/stage-0.md (CONTRIBUTING already links there).

Settle the question the specification flags in section 2: what App Sandbox actually costs here. The claim that distributing outside the App Store 'removes sandbox restrictions on Virtualization.framework' is imprecise, and the README should say something true instead.

Done when: a documented local setup boots a VM, and section 2 of the specification says what is actually the case.

[ispy4you]

Blocked, and the blocker is not technical.

Everything that can be done without an Apple Developer account is done and documented in Docs/stage-0.md: ad-hoc signing carries com.apple.security.virtualization, both the app bundle and the bare tool run guests, debug builds keep get-task-allow, and the sandbox question in section 2 of the specification is settled — the entitlement is available to any developer, and the reason for staying out of the App Store is review policy rather than a missing capability.

What remains needs a paid Apple Developer Program membership ($99/year, OSS-02): Developer ID signing, notarisation through notarytool, and the release pipeline that depends on both (OSS-03, OSS-04). Until someone owns that account, this cannot move — and the account holder should be decided before it is bought, since transferring one afterwards is painful.