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>

config/user_settings.py

@@ -1,40 +1,23 @@
 """
-用户配置模板
+用户配置模板（已废弃，保留用于向后兼容）
 
-此文件包含用户配置的默认值和结构说明。
-实际配置保存在 config/user_settings.json
+此文件已迁移到：
+- config/schema.py - 配置结构定义
+- config/defaults.py - 默认配置值
+
+请使用以下方式导入：
+```python
+from config.defaults import DEFAULT_APP_CONFIG
+from config.schema import AppConfig, ERPConfig, DatabaseConfig
+```
 """
 
-DEFAULT_SETTINGS = {
-    "erp": {
-        "url": "https://68.11.34.30:8082/",
-        "username": "BLDpengqiangqiang",
-        "password": "Cqbld123456.",
-        "headless": True,
-        "ignore_https_errors": True,
-        "auto_close_browser": True
-    },
-    "database": {
-        "server": "192.168.110.114",
-        "database": "CompanyDB",
-        "username": "peng",
-        "password": "Cqbld123456."
-    },
-    "browser": {
-        "headless": True,
-        "ignore_https_errors": True,
-        "auto_close": True
-    },
-    "paths": {
-        "data_dir": "D:/python/playwrite/data/",
-        "production_id_file": "ProductionID.txt",
-        "default_output": "离散备料计划维护_合并.xlsx",
-        "validation_output": "物料状态校验结果.xlsx"
-    },
-    "extraction": {
-        "batch_size": 100,
-        "verbose": True,
-        "auto_convert": True,
-        "merge_batches": True
-    }
-}
+# 为了向后兼容，保留旧版本导入
+from config.defaults import DEFAULT_SETTINGS_DICT as DEFAULT_SETTINGS
+from config.schema import (
+    AppConfig,
+    ERPConfig,
+    DatabaseConfig,
+    PathConfig,
+    ExtractionConfig,
+)