Add manual UAT test guide and indexer/relay deployment docs

[dangershony]

Summary

• Adds src/design/App.Test.Uat/MANUAL-TEST-GUIDE.md — a manual (human-driven) equivalent of the automated App.Test.Uat suite, with step-by-step UI instructions per scenario for testers without a dev environment.
• Adds docker/DEPLOY-INDEXER-AND-RELAY.md — a walkthrough for deploying a new indexer (Mempool.space, for Angornet or mainnet) and a new Nostr relay (strfry), plus a quick local-dev-only option.
• Updates docker/explorers/mainnet/docker-compose.yml:
  • Switches from the old �lockcore/mempool-backend / �lockcore/mempool-frontend fork to the standard, unmodified mempool/backend / mempool/frontend images.
  • Drops the no-longer-needed \ANGOR_ENABLED\ flag.
  • Adds a Fulcrum container for address indexing so mainnet deployments no longer require a separately host-installed Fulcrum instance (Angornet already had this).

Test plan

• \docker compose -f docker/explorers/mainnet/docker-compose.yml config\ validates successfully.
• Docs are informational only (no app code changes); no automated tests apply.