feat(factor): AlphaLab 封装 + Alphalens 分析器

- 新增 alpha_lab.py: AlphaLabSession 类（lazy import vnpy.alpha）
- 新增 analyzer.py: run_factor_analysis + FactorReport（lazy import alphalens）
- 测试: test_alpha_lab.py (2 passed) + test_analyzer.py (3 passed)
- 策略: 本地无 alphalens/polars，函数内 lazy import 避免 ImportError
- 骨架: run_factor_analysis 返回 FactorReport，alphalens 集成待完整实现

sanguo_factor/alpha_lab.py

@@ -0,0 +1,40 @@
+"""AlphaLab session management - lazy import vnpy.alpha to avoid ImportError when alphalens missing."""
+import sys
+import os
+_VNPY_SRC = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "vnpy_v4.4.0"))
+if _VNPY_SRC not in sys.path:
+    sys.path.insert(0, _VNPY_SRC)
+
+
+class AlphaLabSession:
+    """Session manager for vnpy.alpha AlphaLab operations."""
+    
+    def __init__(self, lab_path: str):
+        """
+        Initialize AlphaLab session.
+        
+        Args:
+            lab_path: Path to AlphaLab directory
+        """
+        from vnpy.alpha.lab import AlphaLab
+        
+        self.lab_path = lab_path
+        self.lab = AlphaLab(lab_path)
+    
+    def load_symbols(self, symbols: list[str], start: str, end: str, cfg) -> None:
+        """
+        Load symbol data from database and save to AlphaLab.
+        
+        Args:
+            symbols: List of vt_symbols to load
+            start: Start date (YYYY-MM-DD)
+            end: End date (YYYY-MM-DD)
+            cfg: Database configuration object
+        """
+        from sanguo_data.datareader import read_db_daily
+        from .data_adapter import save_alpha_lab_data
+        
+        for symbol in symbols:
+            bars = read_db_daily(symbol, start, end, cfg)
+            if bars:
+                save_alpha_lab_data(bars, self.lab_path)