feat: 10-band EQ, connection indicator, new icon (v1.5.0)

### 10-Band Graphic Equalizer
- Full EQ in Rust audio engine via EqSource<S> biquad peak filters
- 10 built-in presets + custom preset save/delete
- EqSource::try_seek() implemented — also fixes waveform seek which broke
  silently when EQ was introduced (rodio returned SeekError::NotSupported)
- EQ state persisted in localStorage, synced to Rust on startup

### Connection Indicator
- LED in header (green/red/pulsing) with server name and LAN/WAN label
- Offline overlay with retry button when server is unreachable
- useConnectionStatus hook

### New App Icon
- New logo (logo-psysonic.png) applied across Login, Sidebar, Settings,
  README and all Tauri platform icons (Windows, macOS, Linux, Android, iOS)

### Now Playing Page
- New /now-playing route added

### Fixes
- WaveformSeek: mousemove/mouseup on window to fix drag outside canvas

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/hooks/useConnectionStatus.ts

@@ -0,0 +1,76 @@
+import { useState, useEffect, useCallback, useRef } from 'react';
+import { useAuthStore } from '../store/authStore';
+import { pingWithCredentials } from '../api/subsonic';
+
+export type ConnectionStatus = 'connected' | 'disconnected' | 'checking';
+
+export function isLanUrl(url: string): boolean {
+  try {
+    const hostname = new URL(url.startsWith('http') ? url : `http://${url}`).hostname;
+    return (
+      hostname === 'localhost' ||
+      hostname.endsWith('.local') ||
+      /^127\./.test(hostname) ||
+      /^10\./.test(hostname) ||
+      /^192\.168\./.test(hostname) ||
+      /^172\.(1[6-9]|2\d|3[01])\./.test(hostname)
+    );
+  } catch {
+    return false;
+  }
+}
+
+export function useConnectionStatus() {
+  const [status, setStatus] = useState<ConnectionStatus>('checking');
+  const [isRetrying, setIsRetrying] = useState(false);
+  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
+
+  const check = useCallback(async () => {
+    const server = useAuthStore.getState().getActiveServer();
+    if (!server) {
+      setStatus('disconnected');
+      return;
+    }
+
+    if (!navigator.onLine) {
+      setStatus('disconnected');
+      return;
+    }
+
+    const ok = await pingWithCredentials(server.url, server.username, server.password);
+    setStatus(ok ? 'connected' : 'disconnected');
+  }, []);
+
+  const retry = useCallback(async () => {
+    setIsRetrying(true);
+    await check();
+    setIsRetrying(false);
+  }, [check]);
+
+  useEffect(() => {
+    check();
+    intervalRef.current = setInterval(check, 30_000);
+
+    const handleOnline = () => check();
+    const handleOffline = () => setStatus('disconnected');
+
+    window.addEventListener('online', handleOnline);
+    window.addEventListener('offline', handleOffline);
+
+    return () => {
+      if (intervalRef.current) clearInterval(intervalRef.current);
+      window.removeEventListener('online', handleOnline);
+      window.removeEventListener('offline', handleOffline);
+    };
+  }, [check]);
+
+  const server = useAuthStore(s => s.getActiveServer());
+
+  return {
+    status,
+    isRetrying,
+    retry,
+    isLan: server ? isLanUrl(server.url) : false,
+    serverName: server?.name ?? '',
+  };
+}