[MCP Apps] Add appCapabilities.availableDisplayModes

[martinalong]

Do not merge until after #153 is merged (it's stacked on top of that)

Motivation and Context

• Adds availableDisplayModes field to app capabilities so apps can declare which display modes they support
  • This is necessary for when an app is in fullscreen mode, and then the fullscreen modal smoothly transitions to a new widget that appears. In order to do this, it needs to know if the new widget is fullscreenable, which is what this new property helps determine
• Updates the example customer segmentation app to demonstrate fullscreen mode with a toggle button

How Has This Been Tested?

Manually tested

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/ext-apps@195

commit: 5b6ac19