chore: run jest in two worker processes (closes #426)

The test and test:verbose scripts ran jest with one worker per CPU core,
about 47 processes and 7-8 GiB per run on the shared 48-core build host.
They now pass --maxWorkers=2. One process took the suite past the
30-second cap in script/test, so two it is; the cap is unchanged.
make check, the pre-commit hook and script/cibuild all reach jest
through these scripts. The suite timings quoted in the script/test and
Dockerfile comments are updated to match.

Model: opus-5-5

TODO.md

@@ -45,6 +45,15 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-04: `make test` runs jest in two worker processes
+  ([#426](https://git.eeqj.de/sneak/AutistMask/issues/426)). The `test` and
+  `test:verbose` scripts in `package.json` ran `jest --forceExit`, which starts
+  one worker per CPU core: about 47 processes and 7-8 GiB per run on the shared
+  48-core build host. They now pass `--maxWorkers=2`. One process took the suite
+  past the 30-second cap in `script/test`, which is unchanged; two workers stay
+  inside it, though on the busy build host only just. `make check`, the
+  pre-commit hook and `script/cibuild` all run the suite through these scripts.
+
 - 2026-10-04: The error container on each dApp approval screen keeps its height
   when an error appears
   ([#297](https://git.eeqj.de/sneak/AutistMask/issues/297)). `#approve-tx-error`