fix(docs): prevent API reference title from inheriting child tag description overview page

[devin-ai-integration]

Description

Refs: Related to fern-platform#9488

When tag-description-pages: true is set on an API reference, the top-level API reference title (e.g., "Salesforce Platform APIs") becomes clickable because it inherits the first child tag section's overviewPageId. This is undesirable — the tag description overview pages belong to the individual folder/tag sections, not the parent API reference.

Changes Made

• Added a guard (!this.apiSection.tagDescriptionPages) to the overviewPageId inheritance logic in ApiReferenceNodeConverter.get(). When tag-description-pages is enabled, the parent API reference no longer inherits a child apiPackage's overviewPageId, keeping the top-level title as a non-clickable section header.
• Added a unit test in tag-description-pages.test.ts that asserts overviewPageId is undefined on the ApiReferenceNode when tagDescriptionPages is enabled, and verifies child apiPackage nodes still retain their own overviewPageId values.

Testing

• Existing unit tests pass (44/44 in @fern-api/docs-resolver)
• Unit test added: "does not inherit child tag overviewPageId when tag-description-pages is enabled" — verifies node.overviewPageId is undefined at the API reference level while child apiPackage nodes still have overview pages

rec-fe3b396175c74cc5af878f7d163b4aca-edited.mp4

Human Review Checklist

• Behavioral change for existing users: Any API reference with tag-description-pages: true will no longer have a clickable top-level title (unless an explicit summary/overview page is configured). Verify this is acceptable.
• Flattened case: The old inheritance also applied when the API reference was flattened (comment mentioned DocsDefinitionResolver.toSectionNode() would inherit it). Confirm the flattened case doesn't need special handling.
• No opt-out path: Users who want the old behavior (parent inherits first child's overview) while also using tag-description-pages would need to set an explicit summary on the API reference. Confirm this is reasonable.

Link to Devin session: https://app.devin.ai/sessions/1784b5d69de24f4fbaff5f83675e255e

[devin-ai-integration]

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