PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

OpenAPI 3.2 added three new fields to the Tag Object: parent, kind, and summary. PR #3725 added support for parent and kind, but summary was not included.

Per the OpenAPI 3.2 spec:

summary | string | A short summary of the tag, used for display purposes.

What is the new behavior?

• TagObject interface now includes optional summary field.
• DocumentBuilder.addTag() accepts summary in its 4th-parameter options object, alongside the existing parent and kind.

const config = new DocumentBuilder()
  .addTag('account-updates', 'Account update operations', undefined, {
    summary: 'Account Updates'
  })
  .build();

ApiTagOptions and the @ApiTags() decorator are intentionally not extended in this PR — their hierarchy metadata (parent/kind) is currently discarded (see the existing tests in test/decorators/api-use-tags.decorator.spec.ts which assert this). I'll open a separate issue for that so it can be discussed independently.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Refs #3725.