feat: add Query.relationship helper

[abnegate]

Summary

Adds Query.relationship to generated SDKs so clients can constrain populated related documents.

Query.relationship('comments', [
    Query.equal('approved', true),
    Query.orderDesc('$createdAt'),
    Query.limit(25),
])

This matches Query::relationship() / TYPE_RELATIONSHIP in utopia-php/database#968.

The helper takes a relationship attribute and inner queries (filters, order, select, pagination), then serializes them as nested query objects — the same shape as Query.elemMatch.

Languages

PHP, Web/Node, Deno, React Native, Dart/Flutter, Python, Ruby, Kotlin/Android, .NET/Unity, Swift/Apple, Go, Rust.

Skills docs include the new helper.

Test plan

• Generated PHP Query::relationship unit test (8 assertions)
• Generated PHP Pint
• Generated Go gofmt
• E2E query-helper expectation added for every language that already tests elemMatch
• CI on this PR

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the new helper is consistently implemented and tested across the affected SDK targets.

Summary

• Serializes nested filters, ordering, selection, and pagination queries for populated relationship attributes.
• Adds generated unit coverage and cross-language E2E contract expectations.
• Updates skills documentation for supported language families.

_{Reviews (1) · Last reviewed commit: "feat: add Query.relationship helper"}