refactor: centralize configuration management with type-safe schema

Major changes:
- Add dataclass-based configuration schema with validation (config/schema.py)
- Create centralized config loader and default values (config/defaults.py, config/loader.py)
- Remove duplicate database_config.py, merge into unified structure
- Consolidate browser settings into ERP config
- Add batch_size parameter support to extractor

Bug fixes:
- Fix settings save error by updating config paths (browser.* → erp.*)
- Fix batch_size not being applied in data extraction

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

db/connection.py

@@ -13,7 +13,17 @@ project_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 if project_root not in sys.path:
     sys.path.insert(0, project_root)
 
-from config.database_config import SQL_SERVER_CONFIG
+from config.defaults import DEFAULT_APP_CONFIG
+
+# 从默认配置获取数据库配置
+SQL_SERVER_CONFIG = {
+    'driver': DEFAULT_APP_CONFIG.database.driver,
+    'server': DEFAULT_APP_CONFIG.database.server,
+    'database': DEFAULT_APP_CONFIG.database.database,
+    'username': DEFAULT_APP_CONFIG.database.username,
+    'password': DEFAULT_APP_CONFIG.database.password,
+    'TrustServerCertificate': DEFAULT_APP_CONFIG.database.trust_server_certificate,
+}
 
 
 class DatabaseConnection: