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

.gitignore

@@ -0,0 +1,19 @@
+.nogit/
+
+# artifacts
+coverage/
+public/
+
+# installs
+node_modules/
+
+# caches
+.yarn/
+.cache/
+.rpt2_cache
+
+# builds
+dist/
+dist_*/
+
+#------# custom