fix: RPC server unreachable from outside Docker container

[g-k-s-03]

Problem

The RPC server is hardcoded to 127.0.0.1 in main.py:659:

await rpc_server.start(host="127.0.0.1", port=rpc_port)

The Dockerfile correctly passes --host 0.0.0.0 for the P2P
server via CMD, but the RPC server ignores the --host flag
entirely — it is hardcoded in Python code.

This creates a contradiction:

	Config	Result
P2P server	--host 0.0.0.0 via CMD	reachable from outside
RPC server	hardcoded 127.0.0.1	connection refused
HEALTHCHECK	hits 127.0.0.1:8545	passes inside container
EXPOSE	only declares 9000	8545 not declared

Steps to Reproduce

docker run -p 8545:8545 -p 9000:9000 ghcr.io/stabilitynexus/minichain
curl http://localhost:8545
# connection refused

Expected Behaviour

RPC server should be reachable from outside the container
when -p 8545:8545 is passed.

Proposed Fix

Three small changes:

1. Add --rpc-host CLI argument to main.py (default
   127.0.0.1 for bare metal safety)
2. Use args.rpc_host instead of hardcoded "127.0.0.1"
   on line 659
3. Pass --rpc-host 0.0.0.0 in Dockerfile CMD and add
   EXPOSE 8545