Terrace v0.1.0

Add download page, license, and issue template

Seeds the public releases repo so it has a `main` branch for releases to
anchor to, and a front page that explains the unsigned-installer warning
rather than leaving downloaders to guess.

Source of these files: apps/desktop/distribution/public-repo/ in the
private monorepo, where they are version-controlled alongside the app.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>