arc: Malachite CL is now a proper node component (arc-testnet-node)

Consensus service renamed arc-testnet-consensus -> arc-testnet-node: it is now
generated by templates/nodes/malachite.yml (node: malachite) instead of being
hacked into the arc client template's indexer block. Container body unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

arc/arc/arc-testnet-arc-full.yml

@@ -136,7 +136,7 @@ services:
       - ${NO_SSL:+traefik.http.routers.arc-testnet-arc-full.rule=Path(`/arc-testnet`) || Path(`/arc-testnet/`)}
       - traefik.http.routers.arc-testnet-arc-full.middlewares=arc-testnet-arc-full-stripprefix, ipallowlist
 
-  arc-testnet-consensus:
+  arc-testnet-node:
     image: ${ARC_CONSENSUS_IMAGE:-docker.cloudsmith.io/circle/arc-network/arc-consensus}:${ARC_TESTNET_CONSENSUS_VERSION:-0.7.2}
     user: 0:0
     expose: