feat(client): 所有表格列头加筛选，图标更大靠右对齐

FilterableColumnHeader：
- mainAxisAlignment.spaceBetween 将图标推到列头右侧
- 漏斗图标从 13px 增大到 16px，清除图标 14px

各页面改动：
- batch_tracking：状态/仓库/供应商筛选移入列头，工具栏合并为一行
- finance：类型/往来单位筛选移入列头，工具栏保留月份选择和显示字段
- inventory：仓库筛选从 API 端单选改为客户端多选，移入"仓库"列头
- products：品牌列头加筛选，从加载数据中动态派生选项

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/screens/inventory/batch_tracking_screen.dart

@@ -4,7 +4,7 @@ import '../../core/theme/app_theme.dart';
 import '../../models/inventory.dart';
 import '../../providers/inventory_provider.dart';
 import '../../widgets/data_table_card.dart';
-import '../../widgets/multi_select_dropdown.dart';
+import '../../widgets/multi_select_dropdown.dart' show ColDef, ColumnToggleButton, FilterableColumnHeader;
 
 class BatchTrackingScreen extends ConsumerStatefulWidget {
   const BatchTrackingScreen({super.key});
@@ -135,12 +135,32 @@ class _BatchTrackingScreenState extends ConsumerState<BatchTrackingScreen> {
             (c.minWidth == null || screenWidth >= c.minWidth!))
         .toList();
 
-    final columns = visibleCols
-        .map((c) => DataColumn(
-              label: Text(c.label),
-              numeric: c.key == 'qty' || c.key == 'price',
-            ))
-        .toList();
+    final columns = visibleCols.map((c) {
+      final label = switch (c.key) {
+        'status' => FilterableColumnHeader(
+            text: c.label,
+            options: const ['在售', '已卖出'],
+            selected: _filterStatus,
+            onChanged: (v) => setState(() => _filterStatus = v),
+          ),
+        'warehouse' => FilterableColumnHeader(
+            text: c.label,
+            options: warehouseOptions,
+            selected: _filterWarehouse,
+            onChanged: (v) => setState(() => _filterWarehouse = v),
+          ),
+        'supplier' => FilterableColumnHeader(
+            text: c.label,
+            options: supplierOptions,
+            selected: _filterSupplier,
+            onChanged: (v) => setState(() => _filterSupplier = v),
+          ),
+        _ => Text(c.label),
+      };
+      return DataColumn(
+          label: label,
+          numeric: c.key == 'qty' || c.key == 'price');
+    }).toList();
 
     final rows = records.isEmpty
         ? [
@@ -169,59 +189,24 @@ class _BatchTrackingScreenState extends ConsumerState<BatchTrackingScreen> {
         _page = p;
         _fetch();
       }),
-      toolbar: Column(
-        crossAxisAlignment: CrossAxisAlignment.start,
+      toolbar: Row(
         children: [
-          // Top row: description + refresh + column toggle
-          Row(
-            children: [
-              const Text('已审核入库商品（含库存与销售状态）',
-                  style: TextStyle(
-                      fontSize: 13, color: AppTheme.textSecondary)),
-              const Spacer(),
-              IconButton(
-                icon: const Icon(Icons.refresh, size: 18),
-                onPressed: () => setState(() {
-                  _page = 1;
-                  _fetch();
-                }),
-                tooltip: '刷新',
-              ),
-              const SizedBox(width: 4),
-              ColumnToggleButton(
-                columns: _colDefs,
-                hidden: _hiddenCols,
-                onChanged: (v) => setState(() => _hiddenCols = v),
-              ),
-            ],
+          const Text('已审核入库商品（含库存与销售状态）',
+              style: TextStyle(fontSize: 13, color: AppTheme.textSecondary)),
+          const Spacer(),
+          IconButton(
+            icon: const Icon(Icons.refresh, size: 18),
+            onPressed: () => setState(() {
+              _page = 1;
+              _fetch();
+            }),
+            tooltip: '刷新',
           ),
-          // Filter bar row
-          const SizedBox(height: 6),
-          Row(
-            children: [
-              MultiSelectDropdown(
-                label: '状态',
-                options: const ['在售', '已卖出'],
-                selected: _filterStatus,
-                onChanged: (v) => setState(() => _filterStatus = v),
-              ),
-              const SizedBox(width: 8),
-              if (warehouseOptions.length > 1)
-                MultiSelectDropdown(
-                  label: '仓库',
-                  options: warehouseOptions,
-                  selected: _filterWarehouse,
-                  onChanged: (v) => setState(() => _filterWarehouse = v),
-                ),
-              if (warehouseOptions.length > 1) const SizedBox(width: 8),
-              if (supplierOptions.length > 1)
-                MultiSelectDropdown(
-                  label: '供应商',
-                  options: supplierOptions,
-                  selected: _filterSupplier,
-                  onChanged: (v) => setState(() => _filterSupplier = v),
-                ),
-            ],
+          const SizedBox(width: 4),
+          ColumnToggleButton(
+            columns: _colDefs,
+            hidden: _hiddenCols,
+            onChanged: (v) => setState(() => _hiddenCols = v),
           ),
         ],
       ),