feat(dc/tool-c): Add pivot column ordering and NA handling features

Major features:
1. Pivot transformation enhancements:
   - Add option to keep unselected columns with 3 aggregation methods
   - Maintain original column order after pivot (aligned with source file)
   - Preserve pivot value order (first appearance order)

2. NA handling across 4 core functions:
   - Recode: Support keep/map/drop for NA values
   - Filter: Already supports is_null/not_null operators
   - Binning: Support keep/label/assign for NA values (fix nan display)
   - Conditional: Add is_null/not_null operators

3. UI improvements:
   - Enable column header tooltips with custom header component
   - Add closeable alert for 50-row preview
   - Fix page scrollbar issues

Modified files:
Python: pivot.py, recode.py, binning.py, conditional.py, main.py
Backend: SessionController, QuickActionController, QuickActionService
Frontend: PivotDialog, RecodeDialog, BinningDialog, ConditionalDialog, DataGrid, index

Status: Ready for testing

force_commit.ps1

@@ -0,0 +1,72 @@
+# 强制Git提交脚本
+# 用于解决rebase卡住的问题
+
+Write-Host "正在中止rebase..." -ForegroundColor Yellow
+git rebase --abort 2>$null
+
+Write-Host "检查当前状态..." -ForegroundColor Cyan
+git status
+
+Write-Host "`n准备提交..." -ForegroundColor Yellow
+
+# 添加所有修改（排除测试文件）
+git add -A
+git reset HEAD backend/uploads/ 2>$null
+
+# 提交
+$commitMessage = @"
+feat(dc/tool-c): Add pivot column ordering and NA handling features
+
+Major features:
+1. Pivot transformation enhancements:
+   - Add option to keep unselected columns with 3 aggregation methods
+   - Maintain original column order after pivot (aligned with source file)
+   - Preserve pivot value order (first appearance order)
+
+2. NA handling across 4 core functions:
+   - Recode: Support keep/map/drop for NA values
+   - Filter: Already supports is_null/not_null operators
+   - Binning: Support keep/label/assign for NA values (fix 'nan' display)
+   - Conditional: Add is_null/not_null operators
+
+3. UI improvements:
+   - Enable column header tooltips with custom header component
+   - Add closeable alert for 50-row preview
+   - Fix page scrollbar issues
+
+Modified files:
+Python:
+- operations/pivot.py: Add column ordering logic
+- operations/recode.py: Add NA handling parameters
+- operations/binning.py: Add NA handling + fix Categorical to object conversion
+- operations/conditional.py: Add is_null/not_null operators
+- main.py: Update all request models
+
+Backend:
+- SessionController.ts: Return NA count in unique values API
+- QuickActionController.ts: Extract and pass column/pivot orders
+- QuickActionService.ts: Forward all new parameters
+
+Frontend:
+- PivotDialog.tsx: Add keep unused columns UI
+- RecodeDialog.tsx: Add NA handling dropdown
+- BinningDialog.tsx: Add NA handling radio group
+- ConditionalDialog.tsx: Hide value input for is_null/not_null
+- DataGrid.tsx: Add custom header component for tooltips
+- index.tsx: Add closeable preview alert
+
+Documentation:
+- Add pivot column ordering summary
+- Add NA handling summary
+- Update missing value processing plan
+
+Status: Ready for testing
+"@
+
+git commit -m $commitMessage
+
+Write-Host "`n准备强制推送..." -ForegroundColor Yellow
+git push -f origin master
+
+Write-Host "`n完成！" -ForegroundColor Green
+