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/finance/finance_screen.dart

@@ -4,7 +4,7 @@ import '../../core/theme/app_theme.dart';
 import '../../models/finance.dart';
 import '../../providers/finance_provider.dart';
 import '../../widgets/data_table_card.dart';
-import '../../widgets/multi_select_dropdown.dart';
+import '../../widgets/multi_select_dropdown.dart' show ColDef, ColumnToggleButton, FilterableColumnHeader;
 import '../../widgets/page_scaffold.dart';
 
 class FinanceScreen extends ConsumerWidget {
@@ -161,12 +161,26 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
             (c.minWidth == null || screenWidth >= c.minWidth!))
         .toList();
 
-    final columns = visibleCols
-        .map((c) => DataColumn(
-              label: Text(c.label),
-              numeric: c.key == 'amount' || c.key == 'balance',
-            ))
-        .toList();
+    final columns = visibleCols.map((c) {
+      final label = switch (c.key) {
+        'type' => FilterableColumnHeader(
+            text: c.label,
+            options: typeOptions,
+            selected: _filterType,
+            onChanged: (v) => setState(() => _filterType = v),
+          ),
+        'partner' => FilterableColumnHeader(
+            text: c.label,
+            options: partnerOptions,
+            selected: _filterPartner,
+            onChanged: (v) => setState(() => _filterPartner = v),
+          ),
+        _ => Text(c.label),
+      };
+      return DataColumn(
+          label: label,
+          numeric: c.key == 'amount' || c.key == 'balance');
+    }).toList();
 
     DataCell buildFinanceCell(String key, FinanceRecord r) {
       switch (key) {
@@ -284,44 +298,22 @@ class _FinanceTabState extends ConsumerState<_FinanceTab> {
                 _fetch();
               });
             },
-            toolbar: Column(
-              crossAxisAlignment: CrossAxisAlignment.start,
+            toolbar: Row(
               children: [
-                // Filter bar + month selector + column toggle
-                Row(
-                  children: [
-                    if (typeOptions.length > 1)
-                      MultiSelectDropdown(
-                        label: '类型',
-                        options: typeOptions,
-                        selected: _filterType,
-                        onChanged: (v) => setState(() => _filterType = v),
-                      ),
-                    if (typeOptions.length > 1) const SizedBox(width: 8),
-                    if (partnerOptions.length > 1)
-                      MultiSelectDropdown(
-                        label: '往来单位',
-                        options: partnerOptions,
-                        selected: _filterPartner,
-                        onChanged: (v) =>
-                            setState(() => _filterPartner = v),
-                      ),
-                    const Spacer(),
-                    _MonthSelector(
-                      value: _month,
-                      onChanged: (v) {
-                        _month = v;
-                        _page = 1;
-                        _refetch();
-                      },
-                    ),
-                    const SizedBox(width: 8),
-                    ColumnToggleButton(
-                      columns: _colDefs,
-                      hidden: _hiddenCols,
-                      onChanged: (v) => setState(() => _hiddenCols = v),
-                    ),
-                  ],
+                const Spacer(),
+                _MonthSelector(
+                  value: _month,
+                  onChanged: (v) {
+                    _month = v;
+                    _page = 1;
+                    _refetch();
+                  },
+                ),
+                const SizedBox(width: 8),
+                ColumnToggleButton(
+                  columns: _colDefs,
+                  hidden: _hiddenCols,
+                  onChanged: (v) => setState(() => _hiddenCols = v),
                 ),
               ],
             ),