feat(ui): 增加视觉 token 与统一导航

lib/core/widgets/app_bottom_nav.dart

@@ -0,0 +1,109 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/material.dart';
+
+import '../theme/app_colors.dart';
+import '../theme/app_dimens.dart';
+
+/// One destination rendered by [AppBottomNav].
+class AppBottomNavItem {
+  const AppBottomNavItem({
+    required this.tabKey,
+    required this.icon,
+    required this.selectedIcon,
+    required this.label,
+    required this.onTap,
+    this.selected = false,
+  });
+
+  final Key tabKey;
+  final IconData icon;
+  final IconData selectedIcon;
+  final String label;
+  final VoidCallback onTap;
+  final bool selected;
+}
+
+/// Shared bottom navigation used by all root tabs and the player fallback.
+class AppBottomNav extends StatelessWidget {
+  const AppBottomNav({
+    super.key,
+    required this.items,
+    this.backgroundColor = AppColors.bar,
+  });
+
+  final List<AppBottomNavItem> items;
+  final Color backgroundColor;
+
+  @override
+  Widget build(BuildContext context) => SafeArea(
+    top: false,
+    child: Container(
+      height: AppDimens.navHeight,
+      decoration: BoxDecoration(
+        color: backgroundColor,
+        border: const Border(
+          top: BorderSide(color: AppColors.outlineVariantDark),
+        ),
+      ),
+      child: Row(
+        children: [for (final item in items) _NavDestination(item: item)],
+      ),
+    ),
+  );
+}
+
+class _NavDestination extends StatelessWidget {
+  const _NavDestination({required this.item});
+
+  final AppBottomNavItem item;
+
+  @override
+  Widget build(BuildContext context) => Expanded(
+    child: Semantics(
+      button: true,
+      selected: item.selected,
+      label: item.label,
+      child: InkWell(
+        key: item.tabKey,
+        onTap: item.onTap,
+        child: ConstrainedBox(
+          constraints: const BoxConstraints(minHeight: AppDimens.tapTarget),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              AnimatedContainer(
+                duration: const Duration(milliseconds: 160),
+                curve: Curves.easeOut,
+                padding: const EdgeInsets.symmetric(
+                  horizontal: 14,
+                  vertical: 3,
+                ),
+                decoration: BoxDecoration(
+                  color: item.selected ? AppColors.blue : Colors.transparent,
+                  borderRadius: BorderRadius.circular(14),
+                ),
+                child: Icon(
+                  item.selected ? item.selectedIcon : item.icon,
+                  size: AppDimens.navIcon,
+                  color: item.selected ? AppColors.onPrimary : AppColors.muted,
+                ),
+              ),
+              const SizedBox(height: 2),
+              Text(
+                item.label,
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+                style: TextStyle(
+                  fontSize: AppDimens.navLabel,
+                  fontWeight: item.selected ? FontWeight.w700 : FontWeight.w500,
+                  color: item.selected ? AppColors.blueSoft : AppColors.muted,
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    ),
+  );
+}