feat(dc/tool-c): Add missing value imputation feature with 6 methods and MICE

Major features:
1. Missing value imputation (6 simple methods + MICE):
   - Mean/Median/Mode/Constant imputation
   - Forward fill (ffill) and Backward fill (bfill) for time series
   - MICE multivariate imputation (in progress, shape issue to fix)

2. Auto precision detection:
   - Automatically match decimal places of original data
   - Prevent false precision (e.g. 13.57 instead of 13.566716417910449)

3. Categorical variable detection:
   - Auto-detect and skip categorical columns in MICE
   - Show warnings for unsuitable columns
   - Suggest mode imputation for categorical data

4. UI improvements:
   - Rename button: "Delete Missing" to "Missing Value Handling"
   - Remove standalone "Dedup" and "MICE" buttons
   - 3-tab dialog: Delete / Fill / Advanced Fill
   - Display column statistics and recommended methods
   - Extended warning messages (8 seconds for skipped columns)

5. Bug fixes:
   - Fix sessionService.updateSessionData -> saveProcessedData
   - Fix OperationResult interface (add message and stats)
   - Fix Toolbar button labels and removal

Modified files:
Python: operations/fillna.py (new, 556 lines), main.py (3 new endpoints)
Backend: QuickActionService.ts, QuickActionController.ts, routes/index.ts
Frontend: MissingValueDialog.tsx (new, 437 lines), Toolbar.tsx, index.tsx
Tests: test_fillna_operations.py (774 lines), test scripts and docs
Docs: 5 documentation files updated

Known issues:
- MICE imputation has DataFrame shape mismatch issue (under debugging)
- Workaround: Use 6 simple imputation methods first

Status: Development complete, MICE debugging in progress
Lines added: ~2000 lines across 3 tiers

tests/run_tests.bat

@@ -0,0 +1,49 @@
+@echo off
+REM Windows批处理脚本 - 运行缺失值处理功能测试
+
+echo ========================================
+echo 缺失值处理功能 - 自动化测试
+echo ========================================
+echo.
+
+REM 检查Python是否安装
+python --version >nul 2>&1
+if %errorlevel% neq 0 (
+    echo [错误] Python未安装或不在PATH中
+    pause
+    exit /b 1
+)
+
+echo [1/3] 检查Python服务状态...
+curl -s http://localhost:8001/health >nul 2>&1
+if %errorlevel% neq 0 (
+    echo [警告] Python服务未运行，请先启动服务：
+    echo    cd extraction_service
+    echo    python main.py
+    echo.
+    pause
+    exit /b 1
+)
+echo [OK] Python服务运行正常
+echo.
+
+echo [2/3] 检查依赖...
+python -c "import pandas, numpy, requests" >nul 2>&1
+if %errorlevel% neq 0 (
+    echo [警告] 缺少依赖，正在安装...
+    pip install pandas numpy requests
+)
+echo [OK] 依赖检查完成
+echo.
+
+echo [3/3] 运行测试...
+echo.
+python test_fillna_operations.py
+
+echo.
+echo ========================================
+echo 测试完成
+echo ========================================
+pause
+
+