refactor: destroy Snapshot facade

Remove the seven async facade exports (init, track, patch, restore,
revert, diff, diffFull) and the dedicated makeRuntime wrapper from
snapshot/index.ts. Bootstrap now runs svc.init() through BootstrapRuntime
(with Snapshot.defaultLayer added to BootstrapLayer so the service is
resolvable), the debug CLI commands and the three affected test files
(snapshot, revert-compact, project-init-git) call
AppRuntime.runPromise(Snapshot.Service.use(...)) directly.

https://claude.ai/code/session_01VKXRMreuM8EX2g8WRZPNpm