Enhance ActivityPub image attachments with width/height metadata

[Copilot]

What

• ActivityPub attachment payload
  • ApRendererService.renderDocument() now includes image dimensions from DriveFile.properties:
    • width
    • height
• Type surface update
  • Extended ActivityPub object typing (IObject) with optional width?: number / height?: number.
• Coverage
  • Added a focused unit assertion in packages/backend/test/unit/activitypub.ts to verify rendered document dimensions.
• Changelog
  • Added an Unreleased Server entry for this enhancement.

return {
	type: 'Document',
	mediaType: file.webpublicType ?? file.type,
	url: this.driveFileEntityService.getPublicUrl(file),
	name: file.comment,
	width: file.properties?.width,
	height: file.properties?.height,
	sensitive: file.isSensitive,
};

Why

Misskey’s ActivityPub image attachments previously omitted size metadata, which forces federated clients to assume square aspect ratios until media is fetched.
Including width/height aligns Misskey output with common AP implementations and enables better initial remote layout.

Additional info (optional)

• Scope
  • Server-side ActivityPub serialization only; no DB schema or migration changes.
• Compatibility
  • Fields are optional and emitted only when present in file properties.

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[kakkokari-gtyih]

wrong insertion point; append changelog directly in 2026.6.0