Add publishAt regression coverage for shared skill packages

[Copilot]

workspace-public depends on publishAt being persisted and queryable on SkillPackage; if that field falls out of the contract or entity metadata, shared skill listings can silently disappear. This PR adds focused regression coverage around that path and records the patch in a changeset.

• Contracts

  • Add a focused spec for ISkillPackage to keep publishAt visible on the shared skill package shape.

• Entity metadata

  • Add a TypeORM metadata spec for SkillPackage to assert that the inherited publishAt column remains present with the expected timestamptz / nullable configuration.

• Release note

  • Add a patch changeset describing the publishAt protection for workspace-public publishing flows.

const publishAtColumn = getMetadataArgsStorage()
  .filterColumns([SkillPackage, WorkspaceBaseEntity])
  .find(({ propertyName }) => propertyName === 'publishAt')

expect(publishAtColumn).toMatchObject({
  propertyName: 'publishAt',
  options: expect.objectContaining({
    type: 'timestamptz',
    nullable: true
  })
})