Add the authenticated machine funding server

[ameya-deshmukh]

Summary

• expose authenticated loopback-only sUSDC and native-gas funding endpoints
• sign and submit Seismic transactions through Alloy with receipt reconciliation
• enforce Redis-backed idempotency, atomic budgets, recipient limits, and serialized operator nonces
• validate the chain, faucet contract, signer address, and restricted operator role at startup

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo test --workspace --locked (18 tests)
• cargo build --workspace --release --locked

Stack

3 of 4. Depends on #38; next is #40. Split from #35.

Fixes SEI-416 — https://linear.app/seismic-systems/issue/SEI-416/3-machine-funding-add-the-authenticated-funding-server

[linear-code]

SEI-416