Rebuild the review page as a channel strip

The app is about operating something — playing a track and setting a level on
it — but every screen looked like a form. One metaphor now does three jobs.

- Reviewing: a vertical fader beside the text, so the two things you do at
  once stop being a screen apart. Native range input, so keyboard, focus and
  form submission are unchanged; on mobile it lies down and the ticks reverse
- The reveal: everyone's scores as a row of channels. The silhouette of that
  row is the spread, which the stats page can only tell you as a number
- Profiles: given versus received as two faders, the one comparison that says
  something about a person

The player is now a transport: play/pause, a range input for seeking so arrow
keys come free, and a stereo level meter driven by a real AnalyserNode. It is
progressive enhancement — the page ships native audio controls and the script
takes over, so no JS means the browser's own player. The meter is dark until
audio actually plays and stops when it does; reduced motion skips it entirely.

Also: hidden scores are hatched rather than blank, the nav carries the queue
count, "Seuraava jonossa" keeps the loop going after a review, leaderboards
gained level bars and a range bar where divisive is the point, durations read
3:54, both lists can get back to the start, and the admin invite table lists
unused codes instead of silently truncating at 50.

Slogan restored from the original app, three decades on.

admin.go

@@ -29,17 +29,25 @@ type adminMember struct {
 }
 
 type dashboard struct {
-	Invites   []adminInvite
-	Members   []adminMember
-	Songs     []adminSong
-	OpenCount int
+	Invites    []adminInvite
+	SpentCount int
+	Members    []adminMember
+	Songs      []adminSong
+	OpenCount  int
 }
 
 func (a *app) adminDashboard(w http.ResponseWriter, r *http.Request) {
 	var d dashboard
 
+	// Unused invites are the ones with a job to do; spent ones are counted, not listed. Truncating
+	// a list silently reads as "that's all of them".
+	if err := a.pool.QueryRow(r.Context(),
+		`select count(*)::int from invites where not is_valid`).Scan(&d.SpentCount); err != nil {
+		adminError(w, "invites", err)
+		return
+	}
 	rows, err := a.pool.Query(r.Context(),
-		`select id, code, is_valid, created_at from invites order by created_at desc limit 50`)
+		`select id, code, is_valid, created_at from invites where is_valid order by created_at desc`)
 	if err != nil {
 		adminError(w, "invites", err)
 		return