ci: add E2E preflight check for Headlamp connectivity and plugin version (#24)

Adds a diagnostic step before E2E tests that:
- Logs the expected plugin version from package.json
- Verifies Headlamp is reachable (fails fast if not)
- Attempts to list installed plugins for debugging

This surfaces version mismatches and connectivity issues immediately
instead of requiring analysis of cryptic test timeout failures.

Co-authored-by: gandalf-the-greybeard[bot] <gandalf-the-greybeard[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/e2e.yaml

@@ -25,6 +25,36 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
+      - name: Preflight — verify Headlamp connectivity
+        env:
+          HEADLAMP_URL: ${{ secrets.HEADLAMP_URL || 'http://headlamp.kube-system.svc.cluster.local' }}
+        run: |
+          echo "::group::Expected plugin version"
+          EXPECTED=$(node -p "require('./package.json').version")
+          echo "Plugin version in repo: $EXPECTED"
+          echo "::endgroup::"
+
+          echo "::group::Headlamp connectivity"
+          HTTP_CODE=$(curl -s -o /dev/null -w '%{http_code}' --connect-timeout 10 "$HEADLAMP_URL" || true)
+          if [ "$HTTP_CODE" = "000" ]; then
+            echo "::error::Cannot reach Headlamp at $HEADLAMP_URL — E2E tests will fail"
+            exit 1
+          fi
+          echo "Headlamp responded with HTTP $HTTP_CODE at $HEADLAMP_URL"
+          echo "::endgroup::"
+
+          echo "::group::Installed plugins"
+          # Headlamp serves plugin metadata at /plugins — no auth required
+          curl -sf --connect-timeout 10 "$HEADLAMP_URL/plugins" 2>/dev/null \
+            | node -e "
+              const d = require('fs').readFileSync(0,'utf8');
+              try {
+                const plugins = JSON.parse(d);
+                for (const p of plugins) console.log('  ' + p.name + '@' + (p.version||'unknown'));
+              } catch { console.log('  (could not parse plugin list)'); }
+            " || echo "  (plugin list endpoint not available — tests will validate at runtime)"
+          echo "::endgroup::"
+
       - name: Install Playwright browsers
         run: npx playwright install --with-deps chromium