Make read-only components more visually distinctive

For the i15-1 puck selection a component was made read-only (see discussion at https://github.com/DiamondLightSource/atlas/pull/133#discussion_r3721451891) but it's not obvious to a user that this is read-only at a glance. We should make read only components more visually distinctive

Start with the i15-1 puck selection and the read-only component discussed in pull request 133, especially the linked discussion. Identify where the component's visual styling is defined, then make its read-only state visibly distinct and verify the selection still renders correctly.

Written by the indexing model from the issue text.