Reuse the file-editor Shiki extension for the PlanView and SkillsPage editors, gated to non-markdown files. Markdown sources keep the lezer highlighter (its markdown-aware styling is better for editing and there's no Shiki view to match). - PlanView: code files opened through it get Shiki colors; plan .md stays lezer. - SkillsPage: code supporting files get Shiki colors; SKILL.md stays lezer.