Docs: Add Docker to Prerequisites for Scaffold Stellar

[oceans404]

What version are you using?

scaffold-stellar-frontend@0.0.1

What did you do?

1. Followed the "Getting Started" guide for Scaffold Stellar. https://developers.stellar.org/docs/tools/scaffold-stellar#prerequisites
2. Ran stellar scaffold init my-project.
3. Ran npm start to begin local development as instructed by the scaffold output.
4. Note: Docker Desktop was not installed/running on the machine because it was not listed as a prerequisite.

What did you expect to see?

I expected the local development environment (local network, contract deployment, and frontend) to start successfully, or to have been informed in the "Prerequisites" section that a Docker runtime is required for the default local development flow.

What did you see instead?

The process failed immediately during the stellar scaffold watch phase because it could not find a Docker daemon to start the local Stellar node.

Error Output:

[stellar] ℹ️  Starting local Stellar Docker container...
[stellar] ℹ️  Starting local network
[stellar] ⚠️  Failed to connect to Docker daemon at unix:///var/run/docker.sock.
[stellar] ℹ️  Attempting to connect to the default Docker Desktop socket at /Users/steph/.docker/run/docker.sock instead.
[stellar] Failed to start Stellar Docker container: DockerConnectionFailed(BollardErr(HyperLegacyError { err: hyper_util::client::legacy::Error(Connect, Os { code: 2, kind: NotFound, message: "No such file or directory" }) }))
[stellar] ❌ Build error: Failed to start docker container

Suggested Fix:
Add Docker to the list of Prerequisites on the documentation page. While experienced Stellar developers might know the CLI relies on the stellar/quickstart Docker image for local testing, new users following the tutorial for the first time are likely to encounter this "missing dependency" error.