Integrate Atlas as alternative to Blockscout in eth-explorer stack

Once Atlas is production-ready, we should evaluate replacing or offering it alongside Blockscout in the `ev-stacks/stacks/eth-explorer` stack.

**Why:**
- Atlas is purpose-built for ev-node chains — lighter footprint, faster indexing (binary COPY, cursor pagination), and simpler deployment (3 containers vs Blockscout's larger stack).
- Repo: https://github.com/evstack/atlas

**Action items:**
- [ ] Validate Atlas stability and feature coverage against current Blockscout usage
- [ ] Add Atlas as a stack option in `ev-stacks/stacks/eth-explorer`
- [ ] Decide whether to keep Blockscout as a fallback or fully replace

Not urgent — blocked on Atlas reaching confidence for production use.