fix(ci): restore the peer dep the swc install drops, and close a test race (#2040)

Two separate reasons v4.0.0 (#1719) is red.

The SonarQube workflow killed all 616 client test files with "Cannot find module
'@testing-library/dom'". That package is a peer dependency of
@testing-library/react and not a direct dependency of the client, and the step
that installs @swc/core's Linux binary passes --legacy-peer-deps, which tells npm
not to put peer dependencies back when it re-resolves the tree. In test.yml that
step lives in the server job, which never runs client tests, so folding the jobs
into one (#2039) is what brought the two together. It now installs alongside the
swc binary, with its version read from the peer range rather than pinned, and a
one-line resolve check right after fails fast with the module name instead of six
hundred identical failures twenty minutes later.

MAdminStoragePanel's FE-MOB-MSTOR-015 was a genuine race in the test, not in the
panel. Its POST handler incremented postCount, then awaited request.json(), and
only then pushed to migrationPosts — so between the two there was a window where
one POST had been counted but migrationPosts was still empty. The GET handler
reports `migrations: []` for an empty migrationPosts, i.e. "nothing running", so
a poll landing in that window told the queue it was free to start the second
migration, and the waitFor(postCount === 1) above could resolve inside it too.
Parsing before counting closes it. Verified by running the whole mobile suite at
--maxWorkers=8, where it used to surface.

.github/workflows/sonarqube.yml

@@ -45,9 +45,28 @@ jobs:
         # Same reason as test.yml: the lockfile was generated on Windows and omits
         # @swc/core's Linux optional native binary, so npm ci skips it on the
         # runner and the server's SWC transform cannot load.
+        #
+        # @testing-library/dom rides along, and has to. This install re-resolves
+        # the tree, and --legacy-peer-deps means npm does not put peer
+        # dependencies back — @testing-library/dom is a peer of
+        # @testing-library/react and not a direct dependency of the client, so it
+        # was silently dropped and all 616 client test files died on
+        # "Cannot find module". In test.yml this step lives in the server job,
+        # which never runs client tests, so the collision only appears once the
+        # jobs are folded into one. The version is read from the peer range rather
+        # than pinned here, so a bump to @testing-library/react carries over.
         run: |
           SWC_VERSION=$(node -p "require('@swc/core/package.json').version")
-          npm install --no-save --legacy-peer-deps "@swc/core-linux-x64-gnu@$SWC_VERSION"
+          DOM_RANGE=$(node -p "require('@testing-library/react/package.json').peerDependencies['@testing-library/dom']")
+          npm install --no-save --legacy-peer-deps \
+            "@swc/core-linux-x64-gnu@$SWC_VERSION" \
+            "@testing-library/dom@$DOM_RANGE"
+
+      - name: Verify the test toolchain survived that install
+        # Cheap tripwire: if a future dependency bump loses another peer the same
+        # way, this fails here with the name of the module instead of 600
+        # identical test failures twenty minutes later.
+        run: node -e "require.resolve('@testing-library/dom'); require.resolve('@swc/core')"
 
       - name: Build shared
         # Only shared, not the root `build`. server and client run their suites