expose `Query.registrations` with timestamp range

[shrugs]

deferred from the Omnigraph example-query audit.

the subgraph examples cover "latest registrations" and "order by registration/creation time" use cases. the Omnigraph find-domains example can only order domains by NAME (DomainsOrderBy does expose REGISTRATION_TIMESTAMP/REGISTRATION_EXPIRY, but there is no registration-centric top-level entry point).

ask

expose a top-level Query.registrations field returning registrations filterable by a timestamp range (e.g. start / registration timestamp within [from, to]) and orderable by time — supporting "latest registrations" and "registrations in a window" stories.

notes

• requires supporting DB index(es) on the registration timestamp column(s) to keep range queries performant.
• add example queries to packages/ensnode-sdk/src/omnigraph-api/example-queries.ts (and docs meta) once the field exists.

Part of #1360

[coderabbitai]

🔗 Related PRs

#1655 - Registration/Renewal Superceding Refactor [merged]
#1746 - add missing subgraph schema indexes [merged]
#1747 - add missing index on domain name column [merged]

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