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.

CONTEXT.md

@@ -0,0 +1,77 @@
+# Levyraati
+
+A private music review club for about ten friends. Members submit songs and review each other's
+picks; other people's opinions of a song stay hidden until you've written your own.
+
+Identifiers, schema, and routes are English. Rendered text is Finnish only. Each term below carries
+both, so the UI uses one word per concept everywhere.
+
+## Language
+
+**Member** — _jäsen_:
+A person with an account. Every account is a member; there is no other kind.
+_Avoid_: user, käyttäjä, account
+
+**Admin** — _ylläpitäjä_:
+The operator of the installation. Not a member and not an account — a set of credentials on a
+separate surface. Never submits, reviews, or appears in any list of people.
+_Avoid_: admin user, superuser, role
+
+**Invite** — _kutsu_ / **invite code** — _kutsukoodi_:
+A one-time code that permits one registration. Spent only by a registration that succeeds.
+
+**Song** — _kappale_:
+A published piece of music with its converted audio, submitted by a member. A row in `songs` is a
+real song with no qualifier.
+_Avoid_: track, biisi, levy (that's a record, the wrong unit)
+
+**Submission** — _(no Finnish noun; the member sees only the verb_ lähettää _and a status)_:
+A song in flight — uploaded or downloaded, converting, not yet published. It becomes a Song at
+Publish and ceases to exist as a Submission.
+
+**Publish** — _julkaise_:
+The submitter's explicit act of turning a converted Submission into a Song. Never automatic.
+
+**Review** — _arvostelu_:
+One member's score and written verdict on one song. At most one per member per song, and never on
+your own song.
+
+**Reviewer** — _arvostelija_:
+The member who wrote a review. Reviews are never anonymous.
+
+**Score** — _pisteet_:
+An integer 1–100 given in a review.
+_Avoid_: rating, arvosana
+
+**Reveal**:
+Gaining access to other members' opinions of a song by having written your own review of it — or by
+being its submitter. Covers the reviews and the song's average score, on every surface that names a
+song. Enforced in the query, never in the rendering.
+
+Per-song opinion is gated; whole-history aggregate is public. A member's profile shows counts and
+averages over everything they have done, never how they reviewed any particular song.
+
+**Edit window**:
+The 30 minutes after a review's last change, during which its author may edit or delete it. Then the
+review is on the record permanently.
+
+**Locked** (of a song):
+Having at least one review, which freezes its title, artist, and description and prevents the
+submitter deleting it. A live state, not a one-way door: if the last review is deleted, the song is
+editable again.
+
+**Report** — _palaute_:
+A member's free-text note about something broken or annoying, carrying the page they were on. Open
+until the admin resolves it. Deliberately has no category, priority, or severity.
+_Avoid_: ticket, issue, bug, vikailmoitus
+
+**Genre** — _genre_:
+One value from a fixed list, chosen by the submitter.
+_Avoid_: tyylilaji, tag, category
+
+**Ban** — _estä_:
+Ending a member's participation: login refused and live sessions dropped. Their songs and reviews
+remain and continue to count. Reversible.
+
+**Stats** — _tilastot_:
+The always-public leaderboards. The only place aggregate opinion is visible without having reviewed.