fix(ci): #860 integration fixtures survive a busy host port and concurrent runs

Hosted v2-integration run 1224 got past the old fixture-host timeout and
failed one step earlier: "Bind for :::19000 failed: port is already
allocated" — the runner's docker daemon is shared. Fixtures now retry on the
next host port when one is taken (opc-plc keeps host == listen port, as its
advertised endpoint requires) and export the ports actually used; container
names carry the run id so a concurrent run's `down` can't remove them, and a
new `logs` subcommand replaces the workflow's hard-coded name list.

Verified locally: with 19000 squatted, QuestDB moved to 18813/19001 and every
fixture reached ready; logs/down found the suffixed containers.

Claude-Session: https://claude.ai/code/session_01GT67AD99zQQqpLCVm3p7xk

.github/workflows/v2-integration.yml

@@ -81,10 +81,7 @@ jobs:
       - name: fixture logs on failure
         if: failure()
         continue-on-error: true
-        run: |
-          for c in otopcua-ci-mssql otopcua-ci-pg otopcua-ci-questdb otopcua-ci-opcplc otopcua-ci-opcplc-nat; do
-            echo "=== $c ==="; docker logs --tail 40 "$c" 2>&1 || true
-          done
+        run: bash scripts/ci/integration-fixtures.sh logs
       - name: stop fixtures
         if: always()
         continue-on-error: true