Tests pass under heavy host load (closes #233)

vitest runs at most four workers instead of one per core; minWorkers is
set to 1 because vitest 2 rejects a maxWorkers below its default
minWorkers. test/cli/bin.test.ts compiles the sources bin/quak.ts imports
and starts libsodium once, before its tests run. The fake accounts in
test/ente-server.ts and test/thumbnails/thumbnails.test.ts use
libsodium's lowest Argon2id cost, since each login runs the KDF again.

Model: opus-5-5

test/thumbnails/thumbnails.test.ts

@@ -57,8 +57,11 @@ import type { RetryOptions } from "../../src/retry.js";
 
 const TEST_EMAIL = "thumb@example.com";
 const TEST_PASSWORD = "thumbpass";
-const TEST_OPS = 2;
-const TEST_MEM = 64 * 1024 * 1024;
+// The password is stretched at libsodium's lowest Argon2id cost. Each test
+// builds an account and logs in, and at a realistic cost that takes seconds on
+// a loaded host.
+const TEST_OPS = 1;
+const TEST_MEM = 8192;
 const TEST_TIME = 1700000000000000;
 
 interface ThumbMockState {