Project archival: the delete/remove verb is missing end to end

Since the itx-v4 cutover there is deliberately NO way to delete a project — neither on the auth worker, nor on the engine, nor in the UI. The old always-throwing Delete button and deleteProjectServerFn stub were removed rather than left half-implemented. This task adds the real verb.

What's needed#

Auth worker: archive. Projects live in the auth worker's directory (global-unique slugs). Archival should free the slug (or tombstone it) and drop the project from users' claims.
Engine teardown. itx.projects needs a remove/archive verb that tears down the project's engine state (Project DO, streams, dynamic workers) — or at least detaches it so DOs stop being dialable.
UI. Restore a Delete/Archive action on the projects page (apps/os/src/routes/_app/projects/index.tsx) wired to the new verb.

Known call sites waiting on this#

apps/os/src/lib/project-server-fns.ts — comment where deletion was deliberately removed.
apps/os/e2e/test-support/create-test-project.ts — disposable e2e projects cannot be removed; they leak until the stage resets.
apps/os/e2e/tui-test/run.ts — same leak for disposable TUI projects.
apps/os/src/project-directory.ts — related directory gaps noted there (custom-hostname provisioning + a byHostname endpoint) ride along with the auth-worker directory work.
apps/os/src/components/project-settings-panel.tsx / apps/os/src/components/app-sidebar.tsx — custom hostnames (updateConfig/ensureCustomHostname) are part of the same missing project-lifecycle surface.