fix(home): 重绘二级筛选三线图标

docs/plans/PROGRESS.md

@@ -1111,7 +1111,7 @@ $ flutter test
 
 ## 2026-10-22 首页布局对齐修正
 
-- 一级分类页内切换 6 个列表，未选 18/w400、选中 20/w700；二级 chips 与 26 高筛选按钮仅在精选显示。
+- 一级分类未选 18/w400、选中 20/w700；二级 chips 与 26 高透明三线筛选图标仅在精选显示。
 - 四类卡片去底板/描边，封面统一 3:4、8 圆角、行距 10、封底标题间距 6；状态角标为右上角紧凑异形丝带。
 - 标题下方恢复左对齐题材文字，使用 `|` 分隔、灰色小字，与封面状态角标保持独立。
 - 首页搜索栏到一级、一级到二级、二级到网格间距为 8/8/10；非精选 tab 直接以 10 衔接网格。

lib/core/theme/app_colors.dart

@@ -81,6 +81,7 @@ abstract final class AppColors {
   static const textSecondary = Color(0xFF8E8E93);
   static const textTertiary = Color(0xFF9E9E9E);
   static const textTabInactive = Color(0xFFB0B0B0);
+  static const textFilterIcon = Color(0xFF7A7A7E);
 
   /// 原生开屏与冷启动过渡底色。
   static const splashInk = ink;

lib/core/theme/app_dimens.dart

@@ -113,7 +113,8 @@ abstract final class AppDimens {
   static const double homeSecondaryTagRadius = 13;
   static const double homeSecondaryFilterGap = 8;
   static const double homeSecondaryFilterVisualSize = 26;
-  static const double homeSecondaryFilterIcon = 18;
+  static const double homeSecondaryFilterIcon = 16;
+  static const double homeSecondaryFilterStroke = 1.7;
   static const double homePrimaryCategoryGap = 24;
   static const double homeSecondaryTagGap = 14;
   static const double homeSearchTopGap = 0;

lib/pages/home/widgets/home_grid_header.dart

@@ -342,10 +342,12 @@ class HomeGridHeader extends StatelessWidget {
                   child: Center(
                     child: SizedBox.square(
                       dimension: AppDimens.homeSecondaryFilterVisualSize,
-                      child: const Icon(
-                        Icons.filter_list_rounded,
-                        color: AppColors.textTertiary,
-                        size: AppDimens.homeSecondaryFilterIcon,
+                      child: const Center(
+                        child: CustomPaint(
+                          key: Key('home-secondary-filter-icon'),
+                          size: Size.square(AppDimens.homeSecondaryFilterIcon),
+                          painter: _ThreeLineFilterPainter(),
+                        ),
                       ),
                     ),
                   ),
@@ -395,3 +397,26 @@ class HomeGridHeader extends StatelessWidget {
     );
   }
 }
+
+class _ThreeLineFilterPainter extends CustomPainter {
+  const _ThreeLineFilterPainter();
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    final paint = Paint()
+      ..color = AppColors.textFilterIcon
+      ..strokeWidth = AppDimens.homeSecondaryFilterStroke
+      ..strokeCap = StrokeCap.butt;
+    final positions = [
+      size.height * 0.25,
+      size.height * 0.5,
+      size.height * 0.75,
+    ];
+    for (final y in positions) {
+      canvas.drawLine(Offset(0, y), Offset(size.width, y), paint);
+    }
+  }
+
+  @override
+  bool shouldRepaint(_ThreeLineFilterPainter oldDelegate) => false;
+}

test/home/home_preview_layout_test.dart

@@ -98,14 +98,22 @@ void main() {
       tester.getSize(find.byKey(const Key('home-grid-filter'))),
       const Size.square(AppDimens.tapTarget),
     );
-    final filterIcon = tester.widget<Icon>(
-      find.descendant(
-        of: find.byKey(const Key('home-grid-filter')),
-        matching: find.byIcon(Icons.filter_list_rounded),
-      ),
+    final filterIcon = tester.widget<CustomPaint>(
+      find.byKey(const Key('home-secondary-filter-icon')),
     );
-    expect(filterIcon.size, AppDimens.homeSecondaryFilterIcon);
-    expect(filterIcon.color, AppColors.textTertiary);
+    expect(
+      filterIcon.size,
+      const Size.square(AppDimens.homeSecondaryFilterIcon),
+    );
+    final filterMaterial = tester.widget<Material>(
+      find
+          .ancestor(
+            of: find.byKey(const Key('home-grid-filter')),
+            matching: find.byType(Material),
+          )
+          .first,
+    );
+    expect(filterMaterial.color, AppColors.transparent);
     final searchBox = find.descendant(
       of: find.byKey(const Key('home-search-entry')),
       matching: find.byType(Container),