fix: node info accepts --rpc-url as fallback for --ip

[devrel-ditto]

Summary

Fixes #24 — node info now accepts the global --rpc-url flag as a fallback when --ip is not provided.

Problem

Every command uses --rpc-url for custom endpoints, but node info only accepted --ip:

platform node info --rpc-url http://127.0.0.1:9650  # ❌ --ip is required
platform node info --ip 127.0.0.1                    # ✅ works

Fix

• Check --ip first (backward compatible)
• Fall back to global --rpc-url if --ip not provided
• Error message updated: --ip or --rpc-url is required

The underlying GetNodeInfoWithInsecureHTTP already accepts full URIs, so no changes needed in the node package.

Testing

$ platform node info --rpc-url http://127.0.0.1:9650  # ✅ works now
Node ID:        NodeID-CMGz4CPsWCpvXx7GeftpDFGo8tir2R7mi

$ platform node info --ip 127.0.0.1                    # ✅ still works
Node ID:        NodeID-CMGz4CPsWCpvXx7GeftpDFGo8tir2R7mi

$ platform node info                                   # ✅ clear error
--ip or --rpc-url is required