feat: add core package

Add @puaros/core package with TypeScript configuration, Vitest test setup, and package structure

packages/core/vitest.config.ts

@@ -0,0 +1,28 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+    resolve: {
+        extensions: ['.ts', '.tsx', '.js', '.jsx', '.json'],
+    },
+    test: {
+        globals: true,
+        environment: 'node',
+        coverage: {
+            provider: 'v8',
+            reporter: ['text', 'json', 'html', 'lcov'],
+            exclude: [
+                '**/node_modules/**',
+                '**/dist/**',
+                '**/*.test.ts',
+                '**/*.spec.ts',
+                '**/tests/**',
+            ],
+            thresholds: {
+                lines: 80,
+                functions: 80,
+                branches: 80,
+                statements: 80,
+            },
+        },
+    },
+});