Install: Docker Compose example contradicts bootstrap configuration guidance

## Description

The Docker Compose example in `docs/install/container/docker.md` includes `cratedb03` in the `cluster.initial_master_nodes` list for all three services, which contradicts the earlier quick-start walkthrough narrative.

## Issue Details

The quick-start section states that `crate03` should join the cluster "with no vote" by omitting it from `cluster.initial_master_nodes`. However, the Docker Compose example includes `cratedb03` in this setting for all services:

```yaml
-Ccluster.initial_master_nodes=cratedb01,cratedb02,cratedb03
```

This makes `cratedb03` a voting member, changing the bootstrap behavior and contradicting the guidance.

## Suggested Fix

Either:
1. Remove `cratedb03` from the `cluster.initial_master_nodes` setting in the Compose example to match the walkthrough
2. Update the prose to reflect that all three nodes are initial master nodes

## References

- Pull Request: https://github.com/crate/cratedb-guide/pull/395
- Review Comment: https://github.com/crate/cratedb-guide/pull/395#discussion_r2422851538
- Requested by: @amotl