ci: serialize self-hosted image validate with Web E2E

PR image validate and Playwright shared evoo-ci runners; overlapping
docker builds left E2E signup flakes and hit the 30-minute job cap.

Co-authored-by: cynarAI <cynarAI@users.noreply.github.com>

.github/workflows/playwright.yml

@@ -56,7 +56,7 @@ jobs:
     runs-on: [self-hosted, evoo-ci, Linux]
     timeout-minutes: 30
     concurrency:
-      group: ${{ inputs.publish_report && 'playwright-publication' || format('playwright-{0}', github.run_id) }}
+      group: ${{ inputs.publish_report && 'playwright-publication' || 'evoo-self-hosted-heavy' }}
       cancel-in-progress: false
     steps:
       - uses: actions/checkout@v5

.github/workflows/publish-server-image.yml

@@ -53,6 +53,10 @@ jobs:
     if: github.event_name == 'pull_request'
     runs-on: [self-hosted, evoo-ci, Linux]
     timeout-minutes: 90
+    # Same pool as Web E2E; image builds starve the dev servers Playwright needs.
+    concurrency:
+      group: evoo-self-hosted-heavy
+      cancel-in-progress: false
     permissions:
       contents: read
     strategy: