Optics 0.1.0

A rewrite: Optics is now a native Windows program instead of a self-hosted web app.

Added

• Optics.exe: pick a folder (Browse, typed path, drag and drop, or command line) and see
  every model in it, zip members included, in a sortable, filterable list with a 3D view.
• FBX support through ufbx, with textures: embedded, at the stated path, beside the
  model, in textures/ or ../textures/, or under another image extension; inside zips too
  (docs/textures.md).
• OBJ with .mtl materials and textures.
• A rendered thumbnail on every row of the list, drawn on a worker thread as rows come
  into view.
• optics-check.exe: --selftest, --check (conformance harness, 11/11), and --render,
  which draws a model to PNG with no display.
• Textured sample models generated by tools/make_samples.py (Blender).
• Setup.cmd quick start; GitHub Actions build, self-test and conformance.
• App icon from asset-forge.

Removed

• The Go backend, React frontend, PostgreSQL, Docker files, user accounts and admin.
• Duplicate detection and tags (ROADMAP.md says which are coming back).