arb nitro minimal: prune-cycle model (.prune.yml --init.prune=minimal)

Revert to the prune-cycle model for minimal nodes: the normal compose serves
RPC with no --init.prune, and a generated .prune.yml runs --init.prune=minimal,
driven periodically by prune-if-prunable (same mechanism as pruned/full). Minimal
nodes are seeded from a pruned backup, then pruned to minimal.

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

arb/nitro/arbitrum-one-nitro-minimal-pebble-hash.yml

@@ -62,7 +62,6 @@ services:
       - --http.corsdomain=*
       - --http.port=8545
       - --http.vhosts=*
-      - --init.prune=minimal
       - --metrics
       - --metrics-server.addr=0.0.0.0
       - --metrics-server.port=6070