chore: remove redundant comments and boilerplate across codebase

Strip doc comments, section dividers, HTML comments, and Flutter
template boilerplate that add no informational value. No logic or
behavior changes.

lib/constants/app_info.dart

@@ -1,13 +1,10 @@
 import 'package:flutter/foundation.dart';
 
-/// App version and info constants
-/// Update version here only - all other files will reference this
 class AppInfo {
   static const String version = '4.5.0';
   static const String buildNumber = '127';
   static const String fullVersion = '$version+$buildNumber';
 
-  /// Shows "Internal" in debug builds, actual version in release.
   static String get displayVersion => kDebugMode ? 'Internal' : version;
 
   static const String appName = 'SpotiFLAC Mobile';