Add lyrics: paste, fetch, and read them while reviewing

Lyrics are suggested at submission and never imposed. The conversion worker
makes one LRCLIB lookup with whatever metadata exists, and the waiting page
has a Hae sanoitukset button that re-queries with whatever title and artist
are currently typed — which is the case that matters, since our metadata comes
from ID3 tags and YouTube uploaders. Neither path overwrites typed text.

- lyrics text on both submissions and songs, copied across at publish. Nothing
  has launched, so the column goes into 001_init.sql rather than a migration
- The lock does not cover lyrics: it freezes what the song claims to be, and
  nobody reviewed the lyrics. So the submitter can still fix them afterwards,
  or paste them for an old song a year later
- The review strip gained a second pane: lyrics on the left, review on the
  right, so following the words costs no scrolling. No lyrics means no pane,
  not an empty one. Below 1024px the panes stack
- LRC timestamps are stored but stripped for reading — they belong to the
  player, not the reader
- The lyrics box is capped and scrolls inside itself, so a long song cannot
  stretch the strip past the screen

Fixes a real bug found on the way: saveMetadata cleared any field the request
did not carry, so publishing wiped the lyrics the worker had just fetched.
Fields absent from a request now keep their stored value.

The client identifies itself to LRCLIB as "levyraati" and nothing more.

Tests cover cleanLyrics keeping line breaks, and fetchLyrics against a local
server: synced beats plain, instrumentals and wrong-length takes are skipped,
and a miss is empty with no error.

docs/later.md

@@ -21,28 +21,60 @@ Two things to remember when it happens:
 
 ## Lyrics with scaled autoscroll
 
-Fetch lyrics and scroll them in time with the audio.
+Fetch lyrics and scroll them in time with the audio. Designed and decided (decisions 45), not built.
 
-- **LRCLIB** (`lrclib.net`) is a community database with no API key, and its responses include
-  `syncedLyrics` — real LRC with `[mm:ss.xx]` per-line timestamps — alongside `plainLyrics`. Query by
-  track, artist and duration, all of which are already on the song row. So a decent share of songs
-  need no faked timing at all.
-- **Synced hit** → highlight the current line properly. **Plain hit or manual paste** → distribute
-  lines evenly across `duration_seconds` and scroll the block *continuously without highlighting a
-  line*. Highlighting makes every second of drift read as a bug, and drift is guaranteed — intros and
-  outros alone break a uniform mapping.
+**Coverage, measured 2026-07-31** rather than assumed. An earlier version of this page guessed
+LRCLIB would miss nearly all Finnish music. It does not:
+
+| Search | Results | With `syncedLyrics` |
+|---|---|---|
+| Nightwish | 20 | 20 |
+| Eppu Normaali | 20 | 13 |
+| CMX | 15 | 12 |
+| Popeda | 20 | 8 |
+
+**LRCLIB** (`lrclib.net`) needs no API key. `/api/get` matches on artist, track and duration within
+±2 s and returns `syncedLyrics` — real LRC with `[mm:ss.xx]` per line — alongside `plainLyrics`;
+`/api/search?q=` is the looser fallback. Go's side is `net/http` and `encoding/json`, so the
+dependency budget survives, and it is treated exactly like ffmpeg and yt-dlp: a timeout, allowed to
+fail, never blocking anything.
+
+**Where it happens: at submission, as a suggestion.**
+
+- The worker attempts one automatic lookup after conversion, using whatever metadata exists.
+- The waiting page has a **Hae sanoitukset** button that re-queries with whatever is currently typed
+  in the title and artist fields. That is the answer for messy tags — `Sentenced   Noose` from a
+  YouTube upload will not match until the submitter fixes it, and the automatic attempt would
+  otherwise just look broken.
+- Neither ever overwrites text the submitter has typed. They can accept the suggestion, edit it, or
+  leave the field empty.
+
+**Storage:** one nullable `lyrics text` column on both `submissions` and `songs`, copied across at
+publish. LRC or plain is told apart by whether the first line starts with `[`, so no second column
+and no flag. **Nothing has launched, so this goes into `001_init.sql` rather than a migration 002.**
+
+**Lyrics stay editable after the song locks** — the lock exists so the thing people reviewed stops
+changing, and nobody reviewed the lyrics. It also means someone can paste them for an old song a
+year later, which is when this feature is most useful.
+
+**Playback:**
+
+- **Synced hit** → highlight the current line properly, driven by the transport's `timeupdate`.
+- **Plain hit or manual paste** → distribute lines evenly across `duration_seconds` and scroll the
+  block *continuously without highlighting a line*. Highlighting makes every second of drift read as
+  a bug, and drift is guaranteed — intros and outros alone break a uniform mapping.
 - The Web Animations API does the whole thing including seeking: build the scroll animation with
   `duration_seconds`, `pause()` it, and bind `play`/`pause`/`seeked` on the audio element. No timers,
   no drift accumulation.
 - **Leave a nudge knob** — a ±10 s offset slider, remembered per song in `localStorage`. Uniform
   distribution models a song no real song obeys, and one drag while listening beats any heuristic.
-- Storage: one nullable `lyrics text` column. LRC or plain — tell them apart by whether the first
-  line starts with `[`, so no second column and no flag. Fetched best-effort in the publish worker.
-- **Add a paste box to the submitter's edit form.** The genre list contains *Finnish*,
-  *Experimental* and *Just Plain Weird*; LRCLIB will miss nearly all of it, and for those songs the
-  textarea is the entire feature.
-- Copyright posture is the same as the YouTube note: private app, ten people, written down
-  deliberately.
+
+**Still open:** where the panel lives on the song page. That page's job is now *listen and write*,
+and a scrolling lyrics panel competes with the review textarea for both space and attention — a
+collapsed panel under the player is the starting guess, not a decision.
+
+Copyright posture is the same as the YouTube note: private app, ten people, written down
+deliberately.
 
 ---