refactor(client): 盘点屏斑马行 token 化（修暗色破绽）

盘点明细行无差异时的斑马底 Colors.white/FFFAFAFA → surface/bg，
深色主题 B 下不再泛白。该屏现 0 硬编码色残留。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TSKEiHsvauyxYUW2itzUXX

client/lib/screens/inventory/inventory_check_screen.dart

@@ -444,7 +444,7 @@ class _InventoryCheckScreenState extends ConsumerState<InventoryCheckScreen> {
             ? (diff > 0
                 ? context.tokens.success.withOpacity(0.04)
                 : context.tokens.danger.withOpacity(0.04))
-            : (index.isEven ? Colors.white : const Color(0xFFFAFAFA)),
+            : (index.isEven ? context.tokens.surface : context.tokens.bg),
       ),
       children: [
         Padding(