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.

templates/submission.html

@@ -31,6 +31,28 @@
 
 {{define "saved"}}<span id="saved" class="saved">{{if .}}Tallennettu {{.}}{{end}}</span>{{end}}
 
+<!-- Included by the page and returned alone by the suggestion button, so the markup exists once.
+     hx-include sends the current title and artist, which is the whole point: the lookup uses what
+     the submitter just fixed, not what the tags claimed. -->
+{{define "lyricsfield"}}
+<div id="lyricsfield">
+  <label>Sanoitukset <span class="muted small">(vapaaehtoinen)</span>
+    <textarea name="lyrics" rows="8" maxlength="20000"
+              placeholder="Liitä sanoitukset tähän tai hae ne alta.">{{.Lyrics}}</textarea>
+  </label>
+  <div class="lyricsbar">
+    <button type="button" class="ghost"
+            hx-post="/submit/{{.ID}}/lyrics"
+            hx-include="[name='title'], [name='artist']"
+            hx-target="#lyricsfield" hx-swap="outerHTML">Hae sanoitukset</button>
+    {{if .Found}}<span class="muted small">Löytyi — tarkista ja muokkaa tarvittaessa.</span>{{end}}
+    {{if .Searched}}{{if not .Found}}
+      <span class="muted small">Ei löytynyt. Tarkista nimi ja esittäjä tai liitä sanoitukset itse.</span>
+    {{end}}{{end}}
+  </div>
+</div>
+{{end}}
+
 {{define "content"}}
 <h1>Lähetys</h1>
 
@@ -58,6 +80,7 @@
   <label>Esittely <span class="muted small">(vapaaehtoinen)</span>
     <textarea name="description" rows="5" maxlength="2000">{{.Data.Description}}</textarea>
   </label>
+  {{template "lyricsfield" dict "ID" .Data.ID "Lyrics" .Data.Lyrics}}
   {{template "saved" ""}}
 </form>