feat(core): initial release of SKR03/SKR04 German accounting standards implementation

- Complete implementation of German standard charts of accounts
- SKR03 (Process Structure Principle) for trading/service companies
- SKR04 (Financial Classification Principle) for manufacturing companies
- Double-entry bookkeeping with MongoDB persistence
- Comprehensive reporting suite with DATEV export
- Full TypeScript support and type safety

ts/skr.database.ts

@@ -0,0 +1,39 @@
+import * as plugins from './plugins.js';
+import type { IDatabaseConfig } from './skr.types.js';
+
+let dbInstance: plugins.smartdata.SmartdataDb | null = null;
+
+export const getDb = async (
+  config?: IDatabaseConfig,
+): Promise<plugins.smartdata.SmartdataDb> => {
+  if (!dbInstance) {
+    if (!config) {
+      throw new Error(
+        'Database configuration required for first initialization',
+      );
+    }
+
+    dbInstance = new plugins.smartdata.SmartdataDb({
+      mongoDbUrl: config.mongoDbUrl,
+      mongoDbName: config.dbName || 'skr_accounting',
+    });
+
+    await dbInstance.init();
+  }
+
+  return dbInstance;
+};
+
+export const getDbSync = (): plugins.smartdata.SmartdataDb => {
+  if (!dbInstance) {
+    throw new Error('Database not initialized. Call getDb() first.');
+  }
+  return dbInstance;
+};
+
+export const closeDb = async (): Promise<void> => {
+  if (dbInstance) {
+    await dbInstance.close();
+    dbInstance = null;
+  }
+};