[ermos]

Summary

• Decap "files" collections are now supported instead of ignored: a collection lists fixed files, each with its own fields.
• Files are listed in config order under their label, read in one GraphQL call on GitHub with the drafts. A file missing from the repository opens empty and is created on save.
• They are edited only: creating returns 403 (create is forced to false), deleting is refused except dropping a draft.
• The API resolves the fields of the file from {slug} or ?slug= (AI assistant, autosave), so validation and rendering use the file's own fields.
• i18n on a files collection is refused, seo and relations may use fields of any file.
• UI: the editor uses the file fields and hides "Delete entry". The visual sumigo.yml form gets a Folder / Fixed files switch and a file list, and the YAML completion knows the new keys.
• Docs: new "Files collections" section in the sumigo.yml reference, README and introduction, Decap differences table updated.

Tests

• TestFilesCollectionsResolveTheirFiles: paths, per-file fields, invalid names and paths refused.
• TestFilesCollectionsEditFixedFiles: list with labels, empty missing file, per-file required fields, no create nor delete, unknown file 404.