fix: add timeouts to dagger query, docker info, and portfile loop (#347)

Three unguarded blocking calls caused CI to hang until the 60-min timeout:
- dagger query prune steps had no timeout; || true only catches errors, not hangs
- docker info (added in d905cd6) had no timeout if Docker socket is unresponsive
- until portfile loop in check-dagger spun forever if otel-receiver.py crashed

Fixes: timeout 120 on all dagger query prune calls, timeout 30 on docker info,
and a kill -0 process-alive guard on the portfile until loop with fallback.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/setup_dagger_remote.sh

@@ -24,7 +24,7 @@ for attempt in $(seq 1 $MAX_PROBE_ATTEMPTS); do
     fi
     if [ "$attempt" -eq "$MAX_PROBE_ATTEMPTS" ]; then
         echo "Warning: No Dagger server responded on $host:$port after $MAX_PROBE_ATTEMPTS attempts"
-        if ! docker info >/dev/null 2>&1; then
+        if ! timeout 30 docker info >/dev/null 2>&1; then
             echo "Error: Remote Dagger engine is unavailable AND local Docker daemon is not running."
             echo "Cannot proceed. Ensure either the remote server at $host:$port is accessible"
             echo "or that Docker is running locally (check: sudo systemctl start docker)."