v0.2.0 — exact source position on diagnostics

Added

• Every diagnostic can now carry an exact source position (line and column), not just a bare file path. Message gained a new position: Option<Position> field; the CLI's human-readable output now shows path:line:col when a position is available (--format ids is unaffected). The WASM bindings expose the same Position type.
• Additive only: Report::push_at_pos sits alongside the existing push/push_at methods, which are unchanged. Position is populated at the large majority of check sites; a documented minority (schematron-generated findings, CSS-based checks, ZIP-archive-entry-level checks, and a few "input didn't parse at all" cases) have no coherent position to report and correctly stay None.

Fixed

• frontmatter is a valid EPUB 3 Structural Semantics vocabulary term (sibling to bodymatter/backmatter) but was incorrectly flagged as unknown vocabulary.

Thanks to Kevin Hendricks (author of the Sigil EPUB editor) for the detailed bug report that prompted both of these fixes.

Full changelog: see CHANGELOG.md