test: the browser runs take their engine from BROWSER, and CI runs all three

openApp() launches chromium, firefox or webkit from playwright-core; the smoke
and DOM runs pass in each. CI runs both per engine, WebKit on macOS for
Safari's text shaping. build.target is set explicitly to the browsers the
bundle promises. CLAUDE.md is back under its 120-line budget.

.github/workflows/ci.yml

@@ -44,11 +44,20 @@ jobs:
       - run: npm ci
       - run: npm run test:lo
 
-  # Production build booted in headless Chromium — catches bundling and boot
-  # regressions the jsdom suite cannot see.
-  smoke:
-    runs-on: ubuntu-latest
-    timeout-minutes: 20
+  # Production build booted in the three engines behind the supported browsers
+  # (vite build.target). WebKit runs on macOS: its text shaping there is Safari's.
+  browser:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { browser: chromium, os: ubuntu-latest }
+          - { browser: firefox, os: ubuntu-latest }
+          - { browser: webkit, os: macos-latest }
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 30
+    env:
+      BROWSER: ${{ matrix.browser }}
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -56,6 +65,7 @@ jobs:
           node-version: 20
           cache: npm
       - run: npm ci
-      - run: npx playwright-core install chromium
+      - run: npx playwright-core install --with-deps ${{ matrix.browser }}
       - run: npm run build
       - run: npm run test:smoke
+      - run: npm run test:dom