docs(docs): improve Docker daemon troubleshooting for all platforms (#24922)

Improves the Docker daemon troubleshooting in the quickstart and Docker
install docs:

- Renames the quickstart entry from "Cannot connect to the Docker daemon
on Linux" to cover all platforms.
- Adds a plain-English explanation of what the error means (Docker is
not installed or not running).
- Adds tabbed macOS/Linux/Windows instructions to the quickstart (macOS
and Windows were missing).
- Simplifies the Linux steps to match what Step 1 of the quickstart
already teaches.
- Adds a matching entry to `docs/install/docker.md` with a cross-link to
the quickstart for platform-specific steps.

Supersedes #24907 which was closed without merging.

Fixes https://linear.app/codercom/issue/DEVREL-23

> Generated with [Coder Agents](https://coder.com/agents)

docs/install/docker.md

@@ -96,6 +96,19 @@ Replace `ghcr.io/coder/coder:latest` in the `docker run` command in the
 
 ## Troubleshooting
 
+### Cannot connect to the Docker daemon
+
+If you see an error like:
+
+```text
+Error: Error pinging Docker server: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
+```
+
+Docker is not installed or not running on the host. Install Docker and start the
+daemon before creating a workspace from a Docker-based template. Refer to the
+[quickstart troubleshooting](../tutorials/quickstart.md#cannot-connect-to-the-docker-daemon)
+for platform-specific steps.
+
 ### Docker-based workspace is stuck in "Connecting..."
 
 Ensure you have an externally-reachable `CODER_ACCESS_URL` set. See