docs(flare-entity): add c-chain-indexer-db (MySQL) to the verify-deployment checklist

[pete-csyn]

What

Adds the c-chain-indexer-db (MySQL) container to the Verify deployment success checklist in the "Set Up Flare Entity" guide.

Why

The flare-systems-deployment docker-compose.yaml defines a dedicated c-chain-indexer-db service (image: mysql:9.5.0) as the backing store for the c-chain-indexer:

  c-chain-indexer-db:
    image: "mysql:9.5.0@sha256:57c892dd..."
  ...
  c-chain-indexer:
    ...

After docker compose up -d, this MySQL container is part of the running stack, but the guide's verify checklist lists only system-client, c-chain-indexer, fast-updates-client, ftso-client, and fdc-client — so an operator following the guide has no way to know a MySQL container is expected, and can't confirm it's Up. This addition makes the checklist match what docker ps actually shows.

No other content changed.