refactor: complete migration from .env to YAML configuration

BREAKING CHANGE: Application now uses config.yaml instead of .env files

## Changes:
- Remove dotenv dependency from package.json
- Update all services to use ConfigManager for configuration
- Update tests to use fixed credentials instead of env vars
- Delete obsolete config-manager.test.ts (used old .env API)
- Update documentation (README.md, CLAUDE.md) to reflect new config system

## Configuration Architecture:
- ConfigManager: Centralized YAML configuration with Zod validation
- config.yaml location:
  - Development: Project root (easy to edit and version control)
  - Production: User AppData (persists across updates)
- ERP credentials: Stored in database (dbo_BIPUsers) per user
- Other settings: Stored in config.yaml (database, paths, extraction, etc.)

## Files Modified:
- package.json: Removed dotenv dependency
- cleaner-handler.ts: Use ConfigManager.getDatabaseType()
- run-migration.ts: Read from config.yaml instead of .env
- All integration tests: Use fixed test credentials
- tests/setup.ts: Removed dotenv loading
- README.md, CLAUDE.md: Updated documentation

Migration is complete. Application no longer depends on .env files.

src/main/ipc/cleaner-handler.ts

@@ -124,7 +124,6 @@ export function registerCleanerHandlers(): void {
       return withErrorHandling(async () => {
         let authService: ErpAuthService | null = null
         let dbService: MySqlService | SqlServerService | null = null
-        let erpConfigService: UserErpConfigService | null = null
 
         try {
           // Get ERP configuration from database for current user
@@ -136,9 +135,10 @@ export function registerCleanerHandlers(): void {
             username: erpConfig.username ? 'configured' : 'EMPTY'
           })
 
-          const dbType = process.env.DB_TYPE?.toLowerCase()
+          const configManager = ConfigManager.getInstance()
+          const dbType = configManager.getDatabaseType()
           log.info(
-            `Connecting to ${dbType === 'sqlserver' || dbType === 'mssql' ? 'SQL Server' : 'MySQL'} for order resolution...`
+            `Connecting to ${dbType === 'sqlserver' ? 'SQL Server' : 'MySQL'} for order resolution...`
           )
 
           try {