test(player): wire frontend_test/ into CI

#672 added pkg/service/soundtouchweb/frontend_test/*.test.mjs (Node's
built-in test runner) but never hooked them into anything: not the
Makefile, not any GitHub Actions workflow. They only ran if someone
happened to invoke `node --test` manually, so CI would stay green even
if isSoundTouch10StereoPair or the DeviceDetail notice markup broke.
Added `make test-frontend` and a step in browser-tests.yml (which
already runs the Go-side chromedp player tests) to run them on every
push/PR, matching the pinned actions/setup-node version already used
by update-static-deps.yml.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/browser-tests.yml

@@ -40,10 +40,18 @@ jobs:
       - name: Verify a Chrome/Chromium binary is available
         # chromedp (used by the browsertest-tagged tests) discovers Chrome on
         # PATH or in a standard install location; GitHub's ubuntu-latest
-        # runner image ships Google Chrome preinstalled. Fail fast with a
-        # clear message here instead of a cryptic chromedp allocator error
-        # if that image ever stops including it.
+        # runner image ships Google Chrome preinstalled. Fail fast here with a
+        # clear message instead of a cryptic chromedp allocator error if that
+        # image ever stops including it.
         run: google-chrome --version
 
       - name: Run browser-level player compatibility tests
         run: make test-browser
+
+      - name: Set up Node
+        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version: '24'
+
+      - name: Run frontend unit tests
+        run: make test-frontend