Re-arm a Try-Me Config, making its token resolvable again.

The inverse of expire: re-arms uses_remaining to usage_limit and clears the burn state (used_at, expires_at, briefing_manifest_ref) so the next resolve mints a fresh manifest. Staff operator path — a Mnemom staff caller may re-arm any config in the internal store by id (e.g. the smoke-test demo token), independent of the self-serve opt-in gate. Idempotent. Staff-only. MNE-800. Authorization: Mnemom super-admin (staff) only — the Try-Me config store is a single internal admin surface with no tenant partitioning, so any non-staff caller is rejected (401/403) before the config id is read; there is no cross-tenant object to reach.