feat(core): configure package exports and npm ignore

- Add public API exports from all layers
- Add .npmignore for clean package publishing

packages/core/.npmignore

@@ -0,0 +1,38 @@
+# Source files (only publish dist/)
+src/
+*.ts
+!*.d.ts
+
+# Build artifacts
+tsconfig.json
+tsconfig.*.json
+tsconfig.tsbuildinfo
+*.tsbuildinfo
+
+# Tests
+**/*.spec.ts
+**/*.test.ts
+__tests__/
+coverage/
+
+# Development
+node_modules/
+.env
+.env.*
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# Git
+.git/
+.gitignore
+
+# Other
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.DS_Store

packages/core/src/index.ts

@@ -0,0 +1,4 @@
+export * from './domain';
+export * from './application';
+export * from './infrastructure';
+export * from './shared';