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/migrations/add_data_stats_to_tool_c_session.sql

@@ -0,0 +1,24 @@
+-- 为 DcToolCSession 添加 dataStats 字段
+-- 用于缓存数据统计信息，支持数据探索问答功能
+-- 
+-- 执行方法：psql -d airesearch_v2 -f add_data_stats_to_tool_c_session.sql
+
+\c airesearch_v2
+
+-- 添加字段
+ALTER TABLE dc_schema.dc_tool_c_sessions 
+ADD COLUMN IF NOT EXISTS data_stats JSONB NULL;
+
+-- 添加注释
+COMMENT ON COLUMN dc_schema.dc_tool_c_sessions.data_stats IS '数据统计信息缓存（用于数据探索问答）：{totalRows, columnStats}';
+
+-- 验证
+SELECT column_name, data_type, is_nullable 
+FROM information_schema.columns 
+WHERE table_schema = 'dc_schema' 
+  AND table_name = 'dc_tool_c_sessions' 
+  AND column_name = 'data_stats';
+
+\echo '✅ 字段 data_stats 已成功添加到 dc_tool_c_sessions 表'
+
+