CSS Fallback Resolution for Third-Party Packages

Summary

Third-party community packages (e.g., @refrakt-community/dnd-5e) may ship default CSS as a fallback. When a theme (like Lumina) doesn't provide CSS for a community rune, the pipeline should fall back to the package's own styles/ directory. The resolution order is: theme CSS first, package CSS second.

Currently the SvelteKit plugin's CSS tree-shaking only checks the theme directory. It needs to also check the source package when no theme CSS exists.

Acceptance Criteria

• SvelteKit plugin checks theme's styles/runes/{block}.css first for each rune
• If no theme CSS exists and the rune comes from a third-party package, check the package's styles/runes/{block}.css
• CSS from the winning source is imported into the build
• assembleThemeConfig provenance map is used to locate the source package directory
• refrakt inspect --audit reports which rune CSS comes from the theme vs. package fallback
• Official packages (@refrakt-md/*) are not affected — they ship zero CSS, Lumina provides all their styling

Approach

1. In the SvelteKit plugin's CSS tree-shaking logic, after checking the theme directory and finding no match, consult the provenance map from assembleThemeConfig to find the source package
2. If the source package has a styles/runes/ directory with a matching CSS file, import that as fallback
3. Theme authors can override any package fallback CSS by placing their own file with the same block name in their styles/runes/ directory
4. The audit output in refrakt inspect should distinguish between theme-provided and package-fallback CSS coverage

References

• Community Runes — Specification (Community Runes — Theme Integration)
• Official Rune Packages — Breakout Plan (Official Rune Packages — CSS handling)