Description

Adds a new widget mode where widgets can be registered as Vue components instead of being rendered through the legacy
backend HTML controller/action flow.

This keeps PHP-side widget registration and metadata intact, but lets the frontend render supported widgets directly
without sending a backend widget HTML request. To preserve compatibility, widgetized iframe URLs using
moduleToWidgetize / actionToWidgetize now fall back to a generic Vue bootstrap for client-rendered widgets.

As a first pilot, the Transitions widget was migrated to this new mode.

Changes

• add optional client-rendered widget metadata to WidgetConfig
• expose client widget metadata through API.getWidgetMetadata
• add a direct Vue render path in CoreHome.Widget
• add a ClientWidgetRenderer for loading widget components from plugin UMD bundles
• preserve old widgetize iframe URLs through a fallback in Widgetize.iframe
• avoid backend HTML requests for client-rendered widgets in dashboard widget loading
• migrate Transitions.GetTransitions to the client-rendered widget path
• remove the obsolete server-rendered Transitions widget HTML template/render method

Checklist

• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules

Review

• Functional review done
• Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• New documentation added or existing documentation updated