v5.0.0-alpha.7

feat: generic child theme support

- ModuleManifest/FolderManifest scan the stylesheet directory first, so a
  child theme can ship modules/features and override same-named parent ones
- FeatureRegistry loads runtime/fields from the manifest's resolved _dir
- Vite loader pins hot file, dist URL, and manifest to the template
  directory so an active child theme's dist/ can't shadow parent assets
- New tofino/use_vite_css filter lets a child theme that owns the site-wide
  stylesheet build disable the parent's CSS while keeping its JS
- Sprite output and [svg] shortcode resolve child-first via get_theme_file_path
- render_module plugin comment no longer flags child theme modules
- Dev server discovers sibling child themes (modules/*/module.json), serves
  them via /@fs/ and watches their sources

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>