Make Studio Code aware of theme asset bundling

[gcsecsey]

Related issues

• Fixes STU-2073

How AI was used in this PR

I used Claude to investigate Studio Code's existing theme guardrails, confirm the asset-bundling gap, and draft the guardrail wording. I reviewed and validated the wording and the design decision (awareness over auto-running builds) myself.

Proposed Changes

A user customizing a site on an installed theme reported that Studio Code edited the theme's style.css directly. The existing guardrail already routes design changes into a child theme, but its reasoning only mentioned that a theme update wipes such edits. It missed a second failure mode: many themes serve a compiled or minified stylesheet in production (for example style.min.css, or assets built into build/ or dist/) while the readable source loads only in development, so an edit to the source may never reach the rendered site, and Studio has no build step to recompile it.

• Awareness only, no behavior change. The child-theme default already sidesteps bundling, since a child theme's plain CSS is enqueued directly and never enters the parent's build pipeline, so the agent just needs to know why and decide when to surface it.
• The wording lives in the visual-design skill (loaded during design work) rather than the system prompt, which already covers the child-theme action more tersely.

Testing Instructions

• Ask Studio Code to restyle or add a section to a site whose active theme is an installed theme that ships compiled or minified assets.
• Confirm it makes the change in a child theme (scaffold_theme with parentTheme) rather than editing the installed theme's source files.
• Confirm it can explain, when relevant, that editing the installed theme's source would not reach the rendered site because the theme serves a compiled asset.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[sejas]

LGTM. I confirmed there is no regression in child themes eval by running npm run eval -- --filter-pattern "child theme"