Expand description
Shared primitives for apps::metadata and shells::metadata’s
shine.toml/category loaders: embedded-category-name discovery,
filesystem-category-name discovery, platform filtering, and the
filesystem tree walk + base/overlay merge used to auto-collect files for
categories without an explicit [[files]] list.
Deliberately scoped to just these primitives rather than a full generic
loader: the two domains’ leaf schemas (AppCategory/ShellCategory),
per-file validation rules, and Option-vs-always-Some return shapes
differ enough that forcing them onto one trait-parameterized loader would
be harder to read than the duplication it removes.