新增毛玻璃主题

lib/widgets/frosted_background.dart

@@ -0,0 +1,35 @@
+import 'dart:io';
+import 'dart:ui' as ui;
+import 'package:flutter/material.dart';
+
+/// 毛玻璃主题背景层：封面图 + 模糊 + 深色遮罩
+/// 用 ImageFiltered 模糊静态图片（开销低于 BackdropFilter 实时模糊）
+class FrostedBackground extends StatelessWidget {
+  final String? coverPath;
+
+  const FrostedBackground({super.key, this.coverPath});
+
+  @override
+  Widget build(BuildContext context) {
+    if (coverPath == null || coverPath!.isEmpty) {
+      // 无封面兜底：纯色玻璃底
+      return const ColoredBox(color: Color(0xFF121418));
+    }
+    return Stack(
+      fit: StackFit.expand,
+      children: [
+        ImageFiltered(
+          imageFilter: ui.ImageFilter.blur(sigmaX: 25, sigmaY: 25),
+          child: Image.file(
+            File(coverPath!),
+            fit: BoxFit.cover,
+            errorBuilder: (_, __, ___) =>
+                const ColoredBox(color: Color(0xFF121418)),
+          ),
+        ),
+        // 深色遮罩，保证内容可读
+        const ColoredBox(color: Color(0x73000000)), // 黑 ~45%
+      ],
+    );
+  }
+}