feat: migrate configuration to .env environment variables

This commit implements a complete migration from JSON-based configuration
to .env environment variables, providing better security and flexibility.

Key Changes:
- Add python-dotenv dependency for environment variable support
- Create config/env_loader.py with type conversion utilities
- Add from_env() class methods to all config dataclasses
- Update ConfigLoader to prioritize environment variables
- Add save_to_env() method for .env file management
- Implement database connection factory pattern
- Add base DAO and connection classes for better abstraction
- Support both SQL Server and MySQL with unified interface
- Create migration script (scripts/migrate_to_env.py)
- Update GUI to read/write .env files
- Add comprehensive migration documentation

New Files:
- config/env_loader.py - Environment variable loader
- db/base_connection.py - Base database connection interface
- db/base_dao.py - Base DAO with common utilities
- db/connection_factory.py - Factory for creating connections
- db/mysql_connection.py - MySQL-specific connection
- db/sqlserver_connection.py - SQL Server-specific connection
- db/table_name_converter.py - SQL dialect converter
- scripts/migrate_to_env.py - Configuration migration tool
- docs/ENV_MIGRATION.md - Complete migration guide
- .env.example - Environment variable template

Testing:
- Verified MySQL connection (8.0.44)
- Tested all DAO operations
- Confirmed 150 tables accessible
- Validated configuration loading

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

config/defaults.py

@@ -3,7 +3,7 @@
 """
 默认配置值
 
-定义所有配置项的默认值。
+定义所有配置项的默认值，从环境变量加载。
 """
 from config.schema import (
     ERPConfig,
@@ -12,49 +12,14 @@ from config.schema import (
     ExtractionConfig,
     ValidationConfig,
     AppConfig,
+    SQLServerConfig,
+    MySQLConfig,
+    DatabaseType,
 )
 
 
-# 默认配置
-DEFAULT_APP_CONFIG = AppConfig(
-    erp=ERPConfig(
-        url="https://68.11.34.30:8082/",
-        username="BLDpengqiangqiang",
-        password="Cqbld123456.",
-        headless=True,
-        ignore_https_errors=True,
-        auto_close_browser=True,
-    ),
-    database=DatabaseConfig(
-        server="192.168.110.114",
-        database="CompanyDB",
-        username="peng",
-        password="Cqbld123456.",
-        driver="ODBC Driver 18 for SQL Server",
-        trust_server_certificate="yes",
-    ),
-    paths=PathConfig(
-        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=ExtractionConfig(
-        batch_size=100,
-        verbose=True,
-        auto_convert=True,
-        merge_batches=True,
-        enable_db_persistence=False,  # Disabled by default
-    ),
-    validation=ValidationConfig(
-        data_source="database_full",
-        use_database=True,
-        batch_size=2000,
-        enable_crud_operations=False,
-        default_manager="",
-        match_mode="substring",
-    ),
-)
+# 默认配置 - 从环境变量加载
+DEFAULT_APP_CONFIG = AppConfig.from_env()
 
 
 # 兼容旧版本的字典格式