feat(notes): Add audio recording and playback features

lib/shared/utils/bytes_audio_source.dart

@@ -0,0 +1,56 @@
+import 'dart:typed_data';
+
+import 'package:just_audio/just_audio.dart';
+
+/// A [StreamAudioSource] that plays audio from raw bytes in memory.
+///
+/// This is useful for playing audio data that has been loaded from a network
+/// response or other byte stream, such as server-side TTS audio.
+///
+/// Example:
+/// ```dart
+/// final audioPlayer = AudioPlayer();
+/// final audioBytes = Uint8List.fromList([...]);
+/// await audioPlayer.setAudioSource(
+///   BytesAudioSource(audioBytes, 'audio/mpeg'),
+/// );
+/// await audioPlayer.play();
+/// ```
+class BytesAudioSource extends StreamAudioSource {
+  /// Creates a [BytesAudioSource] from the given bytes and MIME type.
+  ///
+  /// The [mimeType] should be a valid audio MIME type such as:
+  /// - `audio/mpeg` for MP3
+  /// - `audio/wav` for WAV
+  /// - `audio/mp4` or `audio/aac` for AAC/M4A
+  /// - `audio/ogg` for Ogg Vorbis
+  BytesAudioSource(this._bytes, this._mimeType);
+
+  final Uint8List _bytes;
+  final String _mimeType;
+
+  @override
+  Future<StreamAudioResponse> request([int? start, int? end]) async {
+    start ??= 0;
+    end ??= _bytes.length;
+    
+    // Assert valid bounds in debug mode to catch bugs early, but don't
+    // crash in release. just_audio should always pass valid ranges.
+    assert(
+      start >= 0 && start <= _bytes.length,
+      'BytesAudioSource: start ($start) out of bounds [0, ${_bytes.length}]',
+    );
+    assert(
+      end >= start && end <= _bytes.length,
+      'BytesAudioSource: end ($end) out of bounds [$start, ${_bytes.length}]',
+    );
+    
+    return StreamAudioResponse(
+      sourceLength: _bytes.length,
+      contentLength: end - start,
+      offset: start,
+      stream: Stream.value(_bytes.sublist(start, end)),
+      contentType: _mimeType,
+    );
+  }
+}