Attach a dashboard screenshot when you enhance a dashboard with Agent Builder chat

## Summary

When you select Enhance this dashboard on a dashboard in edit mode, Kibana now captures a screenshot of the dashboard grid, uploads it as a chat image attachment, and opens the Agent Builder chat with both the dashboard attachment and the screenshot. Collapsed sections are expanded for the capture, a spinner overlay blocks interaction while capturing, PNG falls back to JPEG above the attachment size limit, and Maps panels render blank in the screenshot. At HEAD, the Enhance this dashboard action is not registered: agent_builder_dashboards/public/plugin.ts hardcodes PRETTIFY_DASHBOARD_ENABLED = false, so the dashboard button never renders.

**Why this needs docs:** Labeled release_note:feature, but the whole Enhance this dashboard (prettify) flow is behind a hardcoded false constant with no setting or feature flag to turn it on, so users cannot reach it in 9.6.0. Document when the constant flips. Confidence kept below 0.8 because the feature is hidden rather than absent.

## Resources

- PR [#288432](https://github.com/elastic/kibana/pull/288432) — [Dashboards in Chat] Capture dashboard screenshot
- Product issue: https://github.com/elastic/kibana/issues/287290

## Availability

| Channel | Details |
|---------|---------|
| **Stack** | v9.6.0 |
| **Serverless** | Sep 7–Sep 11 |
| **Feature flag** | None — active by default |

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## If you chose to document this

[Dashboards and visualizations in Elastic Agent Builder chat](https://www.elastic.co/docs/explore-analyze/ai-features/agent-builder/agent-builder-dashboards-and-visualizations) > How dashboards appear in chat
- **What the docs say:** If you open a new conversation while viewing a dashboard, that dashboard is attached automatically as context, so you can ask about it right away.
- **What to add:** When the Enhance this dashboard action ships (PRETTIFY_DASHBOARD_ENABLED is false at HEAD), add a short subsection: open an existing dashboard in edit mode and select Enhance this dashboard to start a conversation that gets the dashboard and a screenshot of it as attachments, so the agent can see the current layout. Note that collapsed sections are expanded for the capture, that a spinner covers the dashboard while it is captured, and that Maps panels appear blank in the screenshot. Requires Agent Builder access and dashboard write privileges. Do not add until the action is enabled. Applies from the version that enables it and in serverless.