Add CI pipeline, pre-commit hooks, and offline caching

Configure GitHub Actions for linting, typechecking, and testing.
Add Husky and lint-staged for pre-commit checks. Implement API
response caching in AsyncStorage for offline support. Move core
tests to packages/core and add vitest configuration.

packages/core/vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    environment: "node",
+    globals: true,
+  },
+});