Embedded diagrams are not scrollable/pannable on mobile (diagrams not navigable)

### Describe the bug

On mobile devices, embedded diagrams (rendered via the diagrams/image component) are not scrollable or pannable. Example page: https://codex.elastic.dev/r/shared-services-team/processes/incident-management/incident-management-severity-guide

Embedded image: https://codex.elastic.dev/r/shared-services-team/processes/incident-management/images/incident-severity-flowchart.png

When viewing on mobile, touch gestures do not allow panning/scrolling the diagram. On desktop, right-click → open image in new tab shows the full diagram, but mobile users cannot do this easily and cannot navigate the diagram in-place.

### Expected behavior

Users should be able to pan/scroll and zoom diagrams on mobile, or tap to open a navigable/zoomable diagram viewer so the diagram is readable on small screens.

### Steps to reproduce

1. Open the incident management page on a mobile device: https://codex.elastic.dev/r/shared-services-team/processes/incident-management/incident-management-severity-guide
2. Attempt to pan/scroll the embedded diagram (incident-severity-flowchart.png).
3. Observe that touch gestures do not move or zoom the diagram.
4. On desktop, opening the image in a new tab works, but mobile users lack that option and cannot view the diagram at full resolution.

### Tooling

true,false,false

[View original Slack conversation](https://elastic.slack.com/archives/C02762N267P/p1785501618243769?thread_ts=1785501618.243769&cid=C02762N267P)