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.

README.md

@@ -0,0 +1,148 @@
+# Levyraati
+
+A private music review club. Members submit songs — by file upload or YouTube link — and review each
+other's picks on a 1–100 scale. Other people's reviews of a song stay hidden until you've written
+your own.
+
+Invite-only, no public registration. Built for about ten friends.
+
+> **Status:** not built yet. This README describes the app defined in [docs/spec.md](docs/spec.md);
+> commands here are the intended interface, not a record of anything that runs today.
+
+## Docs
+
+| File | What's in it |
+|---|---|
+| [CONTEXT.md](CONTEXT.md) | The glossary — every domain term, in English and Finnish |
+| [docs/spec.md](docs/spec.md) | What the app does: rules, pipeline, routes, API contract, schema |
+| [docs/decisions.md](docs/decisions.md) | Why it is that way. Append-only |
+| [docs/later.md](docs/later.md) | Deliberately not in v1, with the reasoning kept |
+
+## Branches
+
+- **`main`** — released code only. Every commit on it is something that ran in production, or is
+  meant to. Tagged at each release.
+- **`dev`** — current development, and whatever nightly builds get made. Work happens here and
+  reaches `main` by merge at release time.
+
+The app never sends email — there is no verification, no password reset link, and no notifications.
+Members have an address because it is their login and because mail is a planned feature.
+
+## Stack
+
+Go, Postgres, `html/template`, HTMX + Alpine. Audio is converted with ffmpeg and downloaded with
+yt-dlp. One binary, one origin — there is no separate frontend to deploy.
+
+Go dependencies: `pgx/v5` and `golang.org/x/crypto`. No Node, no npm, no bundler.
+
+## Running it
+
+```sh
+cp .env.example .env      # then edit — ADMIN_PASSWORD has no default and the app won't start without it
+docker compose up -d
+```
+
+Migrations apply themselves at startup, before the server accepts connections. The first launch
+creates no users: log into the admin panel and mint an invite.
+
+### Configuration
+
+| Variable | Default | Notes |
+|---|---|---|
+| `DATABASE_URL` | — | `postgres://user:pass@postgres:5432/levyraati` |
+| `ADMIN_USER` | `admin` | Admin panel username |
+| `ADMIN_PASSWORD` | — | **Required.** No default; the app refuses to start without it |
+| `ADDR` | `:8080` | Member-facing listener |
+| `ADMIN_ADDR` | `127.0.0.1:8081` | Admin listener. Keep it on loopback |
+| `STORAGE_DIR` | `./storage` | Audio, avatars, in-flight conversions |
+| `SECURE_COOKIES` | `true` | Set `false` for local development over plain HTTP |
+
+### Local development
+
+```sh
+docker compose up -d postgres
+export DATABASE_URL=postgres://levyraati:levyraati@localhost:5432/levyraati
+export ADMIN_PASSWORD=dev SECURE_COOKIES=false
+go run .
+```
+
+Requires Go 1.22+, plus `ffmpeg`, `ffprobe`, and `yt-dlp` on `PATH`.
+
+Templates, stylesheet, and migrations are embedded with `embed.FS`, so a rebuild is needed to see
+template changes. `go build && ./levyraati` is the loop.
+
+## Admin panel
+
+The admin is **not a user account**. It exists only as `ADMIN_USER` / `ADMIN_PASSWORD`, authenticates
+with HTTP Basic Auth, and is bound to loopback so it is not reachable from the internet. Reach it
+through an SSH tunnel:
+
+```sh
+ssh -L 8081:127.0.0.1:8081 you@server
+# then open http://localhost:8081
+```
+
+From there: mint invites, reset member passwords, ban members, delete songs, read issue reports.
+
+**Lost the admin password?** Edit `.env` and `docker compose restart app`. There is no recovery
+endpoint and no recovery key — the credentials are the environment.
+
+## Operations
+
+### yt-dlp goes stale
+
+yt-dlp needs regular updates to keep working against YouTube. It is installed with
+`pip install -U yt-dlp` at image build time, so rebuilding is how you update it:
+
+```sh
+docker compose build --no-cache app && docker compose up -d app
+```
+
+**Rebuild monthly.** When submissions start failing with download errors, this is the first thing to
+try. Failures are shown to the submitter with the yt-dlp error attached, so they're visible without
+reading logs.
+
+### Logs
+
+```sh
+docker compose logs -f app
+```
+
+JSON to stdout, nothing else. There is no log table and no log viewer in the app.
+
+### Backups
+
+Two paths hold everything:
+
+- `./pgdata` — the database
+- `./storage` — audio files and avatars
+
+Both are bind mounts. `storage/tmp/` is in-flight conversions and is safe to skip; it's cleared on
+startup anyway.
+
+```sh
+docker compose exec postgres pg_dump -U levyraati levyraati | gzip > backup-$(date +%F).sql.gz
+```
+
+### Database shell
+
+```sh
+docker compose exec postgres psql -U levyraati levyraati
+```
+
+## Layout
+
+Go source is flat at the repository root, one package. Beyond that: `templates/` and `static/` are
+embedded assets, `migrations/` holds numbered `.sql` files applied in order at startup, and
+`testdata/` holds the golden JSON files that guard the API contract, plus `ytdlp-noose.json` — a real
+`yt-dlp -J` dump of an ordinary upload, used to test metadata prefill against a video that has no
+`track`, `artist` or `album` at all.
+
+## Notes
+
+Downloading audio from YouTube is against YouTube's terms of service. This is a private app among a
+handful of friends; the decision is deliberate rather than accidental.
+
+## Licence
+
+MIT — see [LICENSE](LICENSE).