cover art color scheme extraction (in background)

refactor text styles to use theme
port over part of album screen

lib/app/ui/theme.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/material.dart';
+
+ThemeData subtracksTheme([ColorScheme? colorScheme]) {
+  final theme = ThemeData.from(
+    colorScheme:
+        colorScheme ??
+        ColorScheme.fromSeed(
+          seedColor: Colors.purple.shade800,
+          brightness: Brightness.dark,
+        ),
+    useMaterial3: true,
+  );
+
+  final text = theme.textTheme;
+  return theme.copyWith(
+    textTheme: text.copyWith(
+      headlineLarge: text.headlineLarge?.copyWith(
+        fontWeight: FontWeight.w800,
+      ),
+      headlineMedium: text.headlineMedium?.copyWith(
+        fontWeight: FontWeight.w700,
+      ),
+      headlineSmall: text.headlineSmall?.copyWith(
+        fontWeight: FontWeight.w600,
+      ),
+    ),
+  );
+}