Follow the song in the lyrics

Synced LRC highlights the playing line, keeps it centred and seeks on click.
Plain text scrolls continuously with a nudge knob instead — a highlight on
guessed timings turns guaranteed drift into what looks like a bug. Seuraa
kappaletta turns following off without losing the highlight, and scrolling by
hand turns it off too.

Fixes the scroll landing in the wrong place (offsetTop measured from a
different coordinate space than the box it was applied to) and the fader
shifting the deck sideways at score 100 (auto-sized grid columns plus a
readout spanning both).

templates/partials/player.html

@@ -1,3 +1,30 @@
+{{/* Two shapes, because timed lyrics and guessed lyrics deserve different treatment.
+     Synced: one element per line with its own timestamp, highlighted as it comes.
+     Plain: one block that scrolls continuously, with a nudge knob, because a highlight on evenly
+     guessed timings turns guaranteed drift into what looks like a bug. */}}
+{{define "lyricsview"}}
+<span class="cap">Sanoitukset</span>
+{{$lines := .LyricLines}}
+{{if $lines}}
+  <div class="lyricsbox synced" data-song="{{.ID}}">
+    {{range $lines}}<p class="lline" data-t="{{.At}}">{{if .Text}}{{.Text}}{{else}}&nbsp;{{end}}</p>{{end}}
+  </div>
+  <label class="follow">
+    <input type="checkbox" checked> Seuraa kappaletta
+    <span class="muted small">— korostus jatkuu, sivu ei vieri</span>
+  </label>
+{{else}}
+  <div class="lyricsbox plain" data-duration="{{.Duration}}" data-song="{{.ID}}">
+    <div class="lscroll">{{lyricstext .Lyrics}}</div>
+  </div>
+  <label class="nudge">
+    Ajoitus
+    <input type="range" min="-10" max="10" step="0.5" value="0" aria-label="Ajoituksen siirto sekunteina">
+    <output>0 s</output>
+  </label>
+{{end}}
+{{end}}
+
 {{define "player"}}
 <!-- Ships with native controls; player.js removes them and drives the same element. No JS means
      the browser's own player, which is plain but complete. -->