Tests pass under heavy host load (closes #233)

The suite timed out when this host was heavily loaded. vitest now runs at most four workers instead of one per CPU core. `test/cli/bin.test.ts` loads the sources `bin/quak.ts` imports and starts libsodium once, before its tests, so no test pays for the first load. The fake accounts in `test/ente-server.ts` and `test/thumbnails/thumbnails.test.ts` stretch their passwords at libsodium's lowest Argon2id cost, since every login stretches them again.

Judgement call: the login, usage, unwrap and KDF tests keep the realistic 64 MiB cost.

Model: opus-5-5

TODO.md

@@ -26,6 +26,14 @@ declares one.
 
 # Completed Steps
 
+- 2026-11-10: The test suite passes on a host under heavy load
+  (https://git.eeqj.de/sneak/quak/issues/233). vitest runs at most four workers
+  instead of one per CPU core. `test/cli/bin.test.ts` compiles the sources
+  `bin/quak.ts` imports and starts libsodium once, before its tests run. The
+  fake accounts of `test/ente-server.ts` and
+  `test/thumbnails/thumbnails.test.ts` stretch their passwords at libsodium's
+  lowest Argon2id cost, since every login stretches the password again.
+
 - 2026-10-26: On an empty cache, `quak helper fix-missing-thumbnails --file`
   stops fetching collections' files once it finds every file it names
   (https://git.eeqj.de/sneak/quak/issues/223). It used to wait for a refresh,