fix audio player freezing and improve UX

Switch WaveSurfer from MediaElement to WebAudio backend to prevent
WKWebView deadlocks that were freezing the entire Tauri app during
audio playback.

Reuse a single WaveSurfer instance across track changes instead of
destroying and recreating on every URL change, which was exhausting
the browser's AudioContext pool.

Other improvements:
- spacebar play/pause with capture phase to prevent history item activation
- drag-to-seek on waveform with silent scrub to avoid WebAudio popping
- slider always mounted to prevent layout shift during track transitions
- play button fills icon, accent bg when playing, loop button accent bg when active
- fix AudioBars animation getting stuck by keying on mode
- remove focus ring on history items
- sync slider position on pause and during seek
- remove title text from player bar
- thicker cursor (3px)

app/src/lib/hooks/useSystemAudioCapture.ts

@@ -1,4 +1,4 @@
-import { useState, useRef, useCallback, useEffect } from 'react';
+import { useCallback, useEffect, useRef, useState } from 'react';
 import { usePlatform } from '@/platform/PlatformContext';
 
 interface UseSystemAudioCaptureOptions {
@@ -94,15 +94,13 @@ export function useSystemAudioCapture({
       const blob = await platform.audio.stopSystemAudioCapture();
 
       // Pass the actual recorded duration
-      const recordedDuration = startTimeRef.current 
-        ? (Date.now() - startTimeRef.current) / 1000 
+      const recordedDuration = startTimeRef.current
+        ? (Date.now() - startTimeRef.current) / 1000
         : undefined;
       onRecordingComplete?.(blob, recordedDuration);
     } catch (err) {
       const errorMessage =
-        err instanceof Error
-          ? err.message
-          : 'Failed to stop system audio capture.';
+        err instanceof Error ? err.message : 'Failed to stop system audio capture.';
       setError(errorMessage);
     }
   }, [isRecording, onRecordingComplete, platform]);