The read-only skill-file markdown viewer stripped the frontmatter and
rendered body-only, so a managed/read-only skill's SKILL.md (for example
the built-in open-knowledge skill) showed none of its name, description,
or other metadata. The editable skill panel already surfaces those fields.

Add a read-only Properties panel above the rendered body in
SkillMarkdownViewer. It parses the frontmatter from the raw text with the
same core helpers the editable PropertyPanel reads at mount, and renders
the shared PropertyDisclosure chrome with static, non-editable rows.
Nested values reuse the existing read-only ComplexValueWidget. No new
translatable strings; the catalogs pick up a reference to the existing
"Properties" message.

GitOrigin-RevId: ad3a9c4e00cd3123983e20ad2f03446ef52ca848