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

backend/prisma/migrations/create_tool_c_session.sql

@@ -32,3 +32,5 @@ COMMENT ON COLUMN dc_schema.dc_tool_c_sessions.columns IS '列名数组 ["age",
 COMMENT ON COLUMN dc_schema.dc_tool_c_sessions.expires_at IS '过期时间（创建后10分钟）';
 
 
+
+

backend/prisma/schema.prisma

@@ -863,6 +863,9 @@ model DcToolCSession {
   encoding  String? @map("encoding") // 文件编码 utf-8, gbk等
   fileSize  Int    @map("file_size") // 文件大小（字节）
   
+  // ✨ 数据统计信息（用于数据探索问答）
+  dataStats Json? @map("data_stats") // 缓存的统计信息：{ totalRows, columnStats: [{name, missingCount, missingRate, uniqueCount, dataType, mean, median}] }
+  
   // 时间戳
   createdAt DateTime @default(now()) @map("created_at")
   updatedAt DateTime @updatedAt @map("updated_at")