feat(scrobble stats): navigator lower bound, clickable rows, android button to top

- Navigator can't step before logging began: the endpoint returns firstPlayedAt
  (MIN(played_at) over all the user's plays, unfiltered by window); web + android
  disable the back arrow once the shown year/month is at/before that first play.
- Top artists/tracks/albums are now clickable → open the artist / album page (web
  navigates and closes the overlay; android navigates via nav routes). Tracks open
  their album.
- Android: moved the 'Meine Statistiken' button to the top of Settings (was at the
  bottom near logout). SW cache -> ns-v70.

Android compileDebugKotlin + web build green; firstPlayedAt verified server-side.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scrobble/scrobble-server.js

@@ -195,6 +195,10 @@ app.get('/scrobble/stats', async (req, res) => {
     `SELECT COUNT(*) AS plays, COALESCE(SUM(duration), 0) AS seconds FROM plays WHERE ${WHERE}`
   ).get(win);
 
+  // Earliest play across ALL of the user's history (unfiltered by window) — lets the client cap the
+  // navigator so you can't step before logging began.
+  const firstPlayedAt = db.prepare('SELECT MIN(played_at) AS t FROM plays WHERE user = :user').get({ user }).t || null;
+
   const topArtists = db.prepare(`
     SELECT MAX(artist) AS name, MAX(artist_id) AS artistId, COUNT(*) AS plays, COALESCE(SUM(duration),0) AS seconds
     FROM plays WHERE ${WHERE} AND artist IS NOT NULL AND artist <> ''
@@ -231,6 +235,7 @@ app.get('/scrobble/stats', async (req, res) => {
   res.json({
     user,
     range: { from, to, tz, bucket },
+    firstPlayedAt,
     totalPlays: totals.plays,
     totalSeconds: totals.seconds,
     topArtists, topAlbums, topTracks, series, byHour,