Report app page lifecycle events through FDC3 for Web protocols to enable DAs to improve HeartBeat Handling

## Enhancement Request

### Use Case

Modern browsers manage page lifecycles (which can throttle or halt javascript execution within an app window when it is hidden). Events are available through the [Page Lifecycle browser API](https://developer.chrome.com/docs/web-platform/page-lifecycle-api) which inform the application of changes in its status.

A browser-based desktop agent cannot currently listen for these events for windows within its scope. The addition of events to the Web Connection Protocol WCP or Desktop Agent Communication Protocol should be explored to allow reporting of state changes to the Desktop Agent which would allow them to develop better logic for handling heartbeats and intent resolution (to throttled or frozen apps).

See #1686 for the original discussion of the issue

Start by reading the discussion in #1686 and the Page Lifecycle browser API reference, then inspect the Web Connection Protocol and Desktop Agent Communication Protocol materials mentioned here. Determine whether and where lifecycle state changes should be reported to a Desktop Agent to improve heartbeat and intent-resolution handling; done requires an agreed protocol-level approach.

Written by the indexing model from the issue text.