ci: shard unit tests four ways

.github/workflows/ci.yaml

@@ -49,7 +49,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        shard: [1, 2]
+        shard: [1, 2, 3, 4]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
       - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
@@ -57,7 +57,7 @@ jobs:
           node-version: "24"
           cache: npm
       - run: npm ci
-      - run: npm test -- --shard=${{ matrix.shard }}/2
+      - run: npm test -- --shard=${{ matrix.shard }}/4
 
   visual:
     name: Visual regression

QUALITY_GATES.md

@@ -62,7 +62,7 @@ isolation). A task is not done until this is green.
   Prettier on staged files at commit; commitlint enforces Conventional Commits.
 - **CI ([`.github/workflows/ci.yaml`](.github/workflows/ci.yaml)):** this
   repository owns every job. `static` (`format:check` + `lint`), `build`
-  (`tsc -b && vite build`), `unit` (`vitest run` in two shards), `visual`
+  (`tsc -b && vite build`), `unit` (`vitest run` in four shards), `visual`
   (Playwright visual), and `governance` (`npm run governance`, with Terraform
   1.16.0) run in parallel. `ci-complete` fails unless all of those jobs
   succeeded and is the required merge-queue check. Live G13 runs on