Provide a UX guideline for FDC3

## Enhancement Request

### Objectives:
- Improve discoverability of available FDC3 actions in apps
- Create a more consistent experience when using FDC3 in different apps to improve the efficiency of FDC3 enabled workflows
- Make the FDC3 'brand' stronger by creating a visual identity that will stand out in FDC3-enabled apps

### Use Case:
- As an end user, I don't have an easy way to identify which actions in my apps will trigger an interop action (broadcast or intent)
- As an end user, I will experience the interoperability very differently depending on which app I'm using, resulting in an inconsistent and frustrating experience
- As an end user, I may not easily discover how to trigger interop workflows in my apps resulting in low usage and reducing the value of FDC3

For example:
- User should know before starting an interop action in an app (e.g. click on a button) that this is an interop action, and what the expected result will be (broadcast, intent, intent on a predefined app), what context data it will use, etc.
- User opening a new FDC3-enabled app should be able to easily discover how this app can interop with others, which context data it can exchange, etc.

Ideally these guidelines will be easy to implement, ie they can be easily adapted to the various design systems of existing apps in order to facilitate adoption.

No files, tests, or entry points are identified. Start by organizing the listed objectives and use cases into a UX guideline covering discoverability, interop-action labeling, expected outcomes, exchanged context data, and adaptable visual identity. Done means the guideline addresses these scenarios and provides implementable recommendations for FDC3-enabled apps.

Written by the indexing model from the issue text.