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.

render.go

@@ -18,8 +18,10 @@ var funcs = template.FuncMap{
 	"fidate": func(t time.Time) string { return t.Local().Format("2.1.2006 15:04") },
 	// Date without the clock: the minute a song was published is noise.
 	"fiday": func(t time.Time) string { return t.Local().Format("2.1.2006") },
-	"score": func(f *float64) string { return strconv.FormatFloat(*f, 'f', 1, 64) },
-	"value": func(f float64) string { return strconv.FormatFloat(f, 'f', 1, 64) },
+	// Lyrics as they are meant to be read: LRC timestamps belong to the player, not the reader.
+	"lyricstext": stripLRC,
+	"score":      func(f *float64) string { return strconv.FormatFloat(*f, 'f', 1, 64) },
+	"value":      func(f float64) string { return strconv.FormatFloat(f, 'f', 1, 64) },
 	// Lets one board partial be called with a title and a list, instead of two near-identical
 	// partials per leaderboard.
 	"dict": func(pairs ...any) map[string]any {