Improve HTML Widget example rendering

[Corina (corinagum)]

Make improvements to HTML Widget example rendering

• Fixes button text rendering in white instead of black
• /hostcontext - as a self-initializing widget (injectWidgetProtocol bypassed by being populated) lacking notifySize() meant that render was too small against actual height of the widget. Removed height: 100% to remove circular measurement.

[Copilot]

Pull request overview

This PR improves the rendering and usability of the examples/html-widgets sample widgets by correcting button text color styling and improving the host-context widget’s sizing behavior so it better matches its actual rendered height in the host.

Changes:

• Explicitly sets button text color to avoid incorrect (white) button label rendering.
• Adjusts host_context widget layout by removing height: 100% on html, body to avoid circular sizing behavior.
• Adds a manual size notification (ui/notifications/size-changed) to help the host correctly size the iframe for self-initializing widgets.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
examples/html-widgets/src/widgets/update_context.py	Sets an explicit button text color to ensure readable button labels.
examples/html-widgets/src/widgets/open_link.py	Sets an explicit button text color to ensure readable button labels.
examples/html-widgets/src/widgets/host_context.py	Removes height: 100% and adds manual size reporting after initialization to improve iframe sizing.