feat: implement unified logging system for GUI components

Add centralized logging mechanism that simultaneously outputs to console
and GUI log components, improving code maintainability and consistency.

Changes:
- Add gui/log_config.py for centralized logging configuration
- Add gui/widgets/log_handler.py as bridge between logging and LogText
- Integrate unified logging into DataExtractionTab and MaterialValidationTab
- Initialize logging system in MainWindow on startup
- Improve error messages in material_status_validator for empty results
- Add documentation for logging mechanism and refactoring

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

gui/main_window.py

@@ -9,6 +9,7 @@ ERP 自动化工具的主窗口，包含多个功能标签页。
 import tkinter as tk
 from tkinter import ttk
 from gui.config_manager import ConfigManager
+from gui.log_config import setup_gui_logging
 from gui.data_extraction_tab import DataExtractionTab
 from gui.material_validation_tab import MaterialValidationTab
 from gui.settings_tab import SettingsTab
@@ -30,6 +31,9 @@ class MainWindow:
         self.session_manager = session_manager
         self.shared_production_ids = []  # 共享的 Production ID 列表
 
+        # 初始化统一日志系统
+        setup_gui_logging()
+
         # 设置窗口属性（包含用户信息）
         user_type_display = "管理员" if session_manager.is_admin() else "用户"
         self.root.title(f"ERP 自动化工具 v1.0 - {session_manager.get_username()} ({user_type_display})")