feat: add Radius Network support (mainnet + testnet)

[TJ-Frederick]

Overview

This PR adds Radius Network (mainnet and testnet) to MCPay. Radius is an EVM-compatible network purpose-built for high-throughput stablecoin payments, with sub-second finality and very low per-tx cost — a natural fit for x402/MCPay micropayment flows.

Changes:

• Bumps viem override and mcpay dep from 2.37.13 to ^2.48.0. viem 2.48.0+ ships native radius and radiusTestnet chain definitions, so no custom chain config is needed.
• Adds radius and radius-testnet cases to the chain switch in packages/js-sdk/src/utils/signer.ts.
• Adds radius and radius-testnet entries to UNIFIED_NETWORKS in apps/app/src/lib/commons/networks.ts, registers SBC (Brale-issued stablecoin, EIP-2612) as a verified stablecoin on both, and extends the UnifiedNetwork / EVMNetwork types.

Network details

Field	Mainnet	Testnet
Name	Radius	Radius Testnet
Chain ID	723487	72344
Native	RUSD (18 decimals)	RUSD (18 decimals)
RPC	https://rpc.radiustech.xyz	https://rpc.testnet.radiustech.xyz
Explorer	https://network.radiustech.xyz	https://testnet.radiustech.xyz
SBC stablecoin	0x33ad9e4BD16B69B5BFdED37D8B5D9fF9aba014Fb (6 decimals, EIP-2612)	same address

SBC (Stablecoin by Brale) is a regulated USD-backed stablecoin issued by Brale and is the canonical stablecoin on Radius. The contract address is identical on mainnet and testnet.

A note on x402

x402Supported is set to false on both Radius entries for now. Radius support landed upstream in x402-foundation/x402#2038 (merged 2026-05-07), but as of this PR the latest x402 npm release (1.2.0, published 2026-04-16) does not yet include those defaults. Once a release with Radius defaults is published, flipping x402Supported: true is a one-line change in both entries — TODO comments mark the spot.

Icon asset

The entries reference /networks/radius.svg, which is not committed in this PR (only apps/app/public/networks/ SVGs already in the repo are referenced by other networks). Happy to provide an SVG in whatever format/dimensions the existing icon set uses — let me know.

References

• Radius x402 integration guide: https://docs.radiustech.xyz/developer-resources/x402-integration
• viem radius chain (added in 2.48.0): https://github.com/wevm/viem/blob/main/src/chains/definitions/radius.ts

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