Expose authenticated settlement reserve identities

[ameya-deshmukh]

Summary

Add two authenticated, read-only endpoints exposing the configured chain, token, and address holding payout liquidity.

• GET /api/internal/base/settlement: Base chain ID, token address, and reserve wallet.
• GET /api/internal/erc20-usdc/settlement: Seismic chain ID, token address, and ERC20 faucet contract (not the admin/reserve EOA).
• Both require the existing machine bearer token and retain existing disabled/unavailable handling.
• No changes to contracts, keys, transfers, budgets, public faucet endpoints, or frontend behavior.

Verification

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --locked: 49 tests passed, including Redis-backed route/authentication and reserve identity coverage.

Compatibility

Additive server update only. No contract redeployment or configuration migration required.

Tracking: SEI-483.

[linear-code]

SEI-483