feat: enable UI actions from AI chat

[djbarnwal]

Adds an opt-in mechanism that allows Rill’s AI agents to trigger approved UI actions in the browser.

Adding capability to support ejection of Rill templates to vega lite spec. (#9850)

UI elements can expose themselves to the agent using a stable data-ai-action identifier. Available actions are sent as transient context with each chat request, and the agent can invoke the new click_ui tool to request an action.

Implementation

• Added the click_ui backend tool for developer and analyst agents.
• Added UIContext and UIAction to the completion API.
• Discover visible, enabled, uniquely identified [data-ai-action] elements when sending a chat message.
• Revalidate actions immediately before clicking them in the browser.
• Added initial actions for:
  • Editing a canvas
  • Starting a dashboard pivot
• Added frontend and backend tests for action discovery, validation, and execution.

Safety

UI actions are explicitly opt-in. The agent cannot use arbitrary CSS selectors or click arbitrary page elements.

An action is available only when it:

• Has a non-empty data-ai-action identifier.
• Is visible and enabled.
• Has a unique identifier on the current page.
• Is outside a data-ai-ignore subtree.
• Is included in the current request’s UI context.

The action is checked again in the browser before the click is performed.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!