Build docs in Docker to avoid host system dependencies

### Is your feature request related to a problem or challenge?

After
- #19280

The docs build would rely on tools being installed on the host machine (e.g. `cargo depgraph`), which makes local setup heavier and less reproducible.

It would be nice to provide a Docker-based workflow for building the docs, so contributors can build everything in an isolated and consistent environment without installing extra dependencies on their system.

Goal: make building docs possible via a simple Docker command with no host setup beyond Docker itself.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by reviewing the existing documentation build workflow and the cargo depgraph dependency mentioned in the issue. Define a Docker-based entry point that builds the documentation without host dependencies, and verify that the documented Docker command succeeds on a clean host with only Docker installed.

Written by the indexing model from the issue text.