Add integration tests against a Palladium regtest node in Docker

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/integration/node/palladium.conf

@@ -0,0 +1,20 @@
+# Palladium node for the integration tests: regtest only, throwaway chain, public credentials.
+# Same RPC user and password as tests/integration/conftest.py and docker-compose.yml.
+rpcuser=plmtest
+rpcpassword=plmtest
+
+# what the ElectrumX server needs from the daemon
+server=1
+txindex=1
+fallbackfee=0.0001
+
+# no peers: a lone regtest node
+listen=0
+discover=0
+dnsseed=0
+
+[regtest]
+rpcport=28443
+# reachable from the other containers and, through the published port, from the host (127.0.0.1 only)
+rpcbind=0.0.0.0
+rpcallowip=0.0.0.0/0