chore(core-events): scaffold package

Create @repo/core-events package skeleton with package.json, tsconfig.json,
vitest.config.ts (using mergeConfig with nodeVitestConfig), eslint.config.js,
turbo.json (tagged core), and AGENTS.md. Register workspace via pnpm install.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-events/tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "extends": "@repo/core-typescript/base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": ".",
+    "paths": {
+      "@/*": ["./src/*"]
+    }
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}