Add appCapabilities.availableDisplayModes to types

- Add `availableDisplayModes` field to `McpUiAppCapabilities` so apps can
  declare which display modes they support
- Change `HostContext.availableDisplayModes` type from `string[]` to
  `McpUiDisplayMode[]` for type safety
- Regenerate schemas

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: martinalong