docs: add DOCKER_HOST guidance for non-default Docker socket paths - #26807

…ooting

When the Docker daemon exposes its socket at a non-default path (common with
Colima and other Docker Desktop alternatives on macOS), the Coder server cannot
connect until DOCKER_HOST points at the right socket. Add this guidance to the
"Cannot connect to the Docker daemon" section of the Docker install guide, and
add a concise cross-referenced entry in the template troubleshooting guide.

Refs: DOCS-466

Filed via Coder Agents on Nick's behalf.

Address review feedback on the DOCKER_HOST troubleshooting guidance:

- Frame the non-default socket case as cross-platform (rootless Docker on
  Linux, plus Colima, Podman, or Rancher Desktop on macOS) instead of
  "Docker Desktop alternatives on macOS".
- Present Colima as one example and add a caveat that tools use different
  default socket paths, with a rootless Docker sample alongside Colima.
- Make persistence shell-agnostic: give the export command, then point at
  the reader's shell startup file instead of assuming Bash or Zsh.
- Correct the Colima socket path to ~/.colima/default/docker.sock.

Filed via Coder Agents on Nick's behalf.

Refs: DOCS-466

Apply docs/.style/style-guide conventions to the DOCKER_HOST
troubleshooting content added in this branch:

- One sentence per line (formatting.md) in both the install guide and
  the template-troubleshooting sections.
- Use "refer to" instead of "see" for the cross-reference in
  troubleshooting.md (word-choice.md).
- Reword the example caveat to state that default socket paths vary by
  tool and the reader should consult their tool's documentation.

Filed via Coder Agents on Nick's behalf.

Refs: DOCS-466