Add node-facts.sh script with JSON node facts emission

Implements node-facts.sh that emits JSON documents for monitoring and inventory:
- Reads COMPOSE_FILE from .env and iterates only those compose files
- Fails fast with JSON error when .env missing or COMPOSE_FILE empty (exit 2)
- Uses --max-time for all curl calls (5s general, 10s for peers)
- Bounded parallel worker count for node processing
- Supports avalanchego, op-node/kona, beacon REST, geth-family, besu, reth/op-reth
- Includes fixture-only test-node-facts.sh with schema validation
- Adds README entry for the new script

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

README.md

@@ -831,6 +831,7 @@ debugging reference, see [VIBE.md](VIBE.md).
 | `force-recreate.sh <name>` | Restart a node |
 | `backup-node.sh <name>` | Create backup |
 | `restore-volumes.sh <name>` | Restore from backup |
+| `node-facts.sh` | Emit JSON node facts documents for monitoring and inventory |
 
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