Apply the default storage quota to every existing workspace

Reads the current value of tenant.default_storage_quota_gb (3-tier resolver: DB > ENV > default) and writes that many GiB into storage_quota for every row in tenants. Bypasses the per-workspace PUT whitelist, which forbids storage_quota edits by Owners. SystemAdmin only. Idempotent — running twice with the same setting is a no-op.