feat(scrobble): web statistics view (Phase 3 UI)

Opens from Settings ("Meine Statistiken") as a self-contained modal overlay
(no router changes). Fetches GET /scrobble/stats and renders: totals tiles
(plays + listening time), a per-bucket play series, top artists/tracks/albums
with mini bars, and a 24h listening clock. Period tabs (all / this year /
last 30 days) switch from/to + bucket. Vanilla inline SVG-free bars, no chart
lib. Reuses .modal-overlay.open + design tokens; sends local tz offset for
day bucketing. Graceful empty/error/unconfigured states. SW cache -> ns-v65.

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

index.html

@@ -712,6 +712,7 @@
         <button style="flex:1;padding:12px;border-radius:9px;font-family:var(--font);font-size:14px;font-weight:600;cursor:pointer;border:none;background:var(--surface2);color:var(--text2)" onclick="closeSettings()">Abbrechen</button>
         <button style="flex:1;padding:12px;border-radius:9px;font-family:var(--font);font-size:14px;font-weight:600;cursor:pointer;border:none;background:linear-gradient(135deg,var(--accent),var(--accent-dark));color:#000" onclick="saveSettings()">Speichern</button>
       </div>
+      <button style="width:100%;padding:10px;border-radius:9px;font-family:var(--font);font-size:13px;font-weight:600;cursor:pointer;background:none;border:1px solid var(--border);color:var(--text2);transition:background .15s" onmouseover="this.style.background='var(--surface2)'" onmouseout="this.style.background='none'" onclick="closeSettings(); openStats()">📊 Meine Statistiken</button>
       <button style="width:100%;padding:10px;border-radius:9px;font-family:var(--font);font-size:13px;font-weight:600;cursor:pointer;background:none;border:1px solid rgba(224,85,85,0.3);color:var(--danger);transition:background .15s" onmouseover="this.style.background='rgba(224,85,85,0.1)'" onmouseout="this.style.background='none'" onclick="confirmDisconnect()">Abmelden</button>
     </div>
   </div>