Add project docs, glossary, and licence

The Nuxt version is being rewritten in Go. This is the design that came out
of it, split by how each part ages:

- CONTEXT.md    glossary, English identifiers and Finnish UI wording
- docs/spec.md  behaviour: rules, submission pipeline, routes, API contract, schema
- docs/decisions.md  why, append-only
- docs/later.md      deliberately not in v1

testdata/ytdlp-noose.json is a real yt-dlp dump used to test metadata
prefill against a video with no track, artist or album tags.

.gitignore

@@ -0,0 +1,4 @@
+/levyraati
+/storage/
+/pgdata/
+.env