feat(dc): Complete Tool C quick action buttons Phase 1-2 - 7 functions

Summary:
- Implement 7 quick action functions (filter, recode, binning, conditional, dropna, compute, pivot)
- Refactor to pre-written Python functions architecture (stable and secure)
- Add 7 Python operations modules with full type hints
- Add 7 frontend Dialog components with user-friendly UI
- Fix NaN serialization issues and auto type conversion
- Update all related documentation

Technical Details:
- Python: operations/ module (filter.py, recode.py, binning.py, conditional.py, dropna.py, compute.py, pivot.py)
- Backend: QuickActionService.ts with 7 execute methods
- Frontend: 7 Dialog components with complete validation
- Toolbar: Enable 7 quick action buttons

Status: Phase 1-2 completed, basic testing passed, ready for further testing

frontend-v2/src/index.css

@@ -9,15 +9,18 @@
   box-sizing: border-box;
 }
 
+/* ✅ 优化5.1：全局字体统一（PingFang中文 + Inter英文）*/
 body {
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
-    'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
-    sans-serif;
+  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei UI", 
+    "Segoe UI", "Inter", "Roboto", sans-serif;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
+  font-feature-settings: "tnum"; /* 等宽数字 */
 }
 
-code {
-  font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
-    monospace;
+/* 等宽字体（代码、数字） */
+code, pre, .font-mono {
+  font-family: "SF Mono", "JetBrains Mono", "Fira Code", Consolas, 
+    "Courier New", monospace;
+  font-variant-numeric: tabular-nums; /* 等宽数字 */
 }