Fix node-facts.sh bugs and add stub-curl integration tests

- Fix grep -qE calls to handle variables starting with '-' (add -- separator)
- Remove local declarations at top level by wrapping main body in main() function
- Replace bounded-worker scheduler with simpler temp file + wait -n pattern
- Fix per-node fan-out to capture function output instead of re-calling
- Add stub-curl integration tests that catch all three original issues
- Add fixture compose files for avalanche, op-node+beacon, geth testing
- Update test path-blacklist.txt to include entry starting with -

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

node-facts-test/path-blacklist.txt

@@ -4,3 +4,4 @@ prysm
 beacon
 nimbus
 ws
+-node