Fix ui-test: set HOME=/root for Firefox in Playwright container

GitHub Actions sets HOME=/github/home (owned by uid 1001) but the
container runs as root. Firefox refuses to launch when HOME is owned
by a different user. Setting HOME=/root fixes the ownership mismatch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: eakmanrq <6326532+eakmanrq@users.noreply.github.com>

Author: eakmanrq

.github/workflows/pr.yaml

@@ -239,6 +239,7 @@ jobs:
         run: npm --prefix web/client run test:e2e
         env:
           PLAYWRIGHT_SKIP_BUILD: '1'
+          HOME: /root
 
   engine-tests-docker:
     needs: changes