fix: close PGlite handle after tests to resolve exit code 100

PGlite's WASM worker kept an open async handle, causing Bun to detect
a resource leak and exit with code 100 despite all tests passing.
Adds a preload script that closes the cached client via afterAll.

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

tests/setup.ts

@@ -0,0 +1,9 @@
+// Bun test preload: close PGlite WASM worker after each file to prevent exit code 100 (leaked handles).
+import { afterAll } from "bun:test";
+import { cachedClient } from "./helpers/db.ts";
+
+afterAll(async () => {
+	if (cachedClient) {
+		await cachedClient.close();
+	}
+});