v0.2.0 — structural diagnostics

Adds the same structural summary the Glyphs and RoboFont plugin dialogs show in their size-estimate strip:

• --verbose mode prints ~38 KB · 5 instances · 3 ax · 1 pinned per output line on stderr (stdout stays xargs-friendly with bare file paths).
• --json mode now includes a diagnostics array alongside written, with {path, sizeBytes, instances, axes, pinned} per output. Useful for build pipelines that want to assert on file size or axis-pinning.

Master count is intentionally omitted — the engine doesn't expose post-instancer master geometry through the public API. Test suite green: 91/91.