Document the saved-view file format and every system frontmatter key

The View Filters reference covers the ideas but not the YAML format. It should list: the keys: name, icon, color, order, sort, listPropertiesDisplay, filters, and presentation from ADR 0144 the ten operators, and regex the built-in fields: type, status, title, filename, archived, favorite, body the sort formats, including property::asc ADR 0040 still says views live in .laputa/views/, but the app reads views/. The Frontmatter Fields reference leaves out keys the app reads (src-tauri/src/frontmatter/keys.rs): _archived, _favorite, _organized, _sort, template, visible and view. View files silently ignore unknown keys. A warning in the view editor would catch mistakes early.