Add a chapter to demonstrate implementation of a Featured App Activity Markers

The new feature "Featured App Activity Markers" was recently rolled out and there is interest from app developers how to implement this. It is described in https://github.com/global-synchronizer-foundation/cips/blob/main/cip-0047/cip-0047.md.

It may be suitable to be an SCU example.

Some reference code can be found at https://github.com/hyperledger-labs/splice/blob/edb2291be31694b9e55eba1ebb607c4eca1a1dbb/daml/splice-api-featured-app-v1/daml/Splice/Api/FeaturedAppRightV1.daml#L4

Start by reading CIP-0047 and the referenced FeaturedAppRightV1.daml code to understand the Featured App Activity Markers feature and its implementation context. Identify the appropriate quickstart chapter or SCU example location, then document a working implementation path for app developers; done means the chapter clearly demonstrates the feature end to end.

Written by the indexing model from the issue text.