DEVX-155: fix: kill existing dockerd before starting /dev/shm/docker daemon

The CI container's pre-existing dockerd (v29.5.3) uses the default
data root on the 38G overlay (100% full). Kill it before starting
the new dockerd with --data-root /dev/shm/docker (16G tmpfs).

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

src/devx/molecule/start_docker.py

@@ -223,6 +223,16 @@ def start_docker_daemon(timeout: int = DEFAULT_TIMEOUT) -> bool:
 
     click.echo(_("Host Docker not available, starting local dockerd..."))
 
+    # Kill any existing dockerd that's using the default data root on the
+    # CI container's overlay (38G, often 100% full). The new dockerd will
+    # use /dev/shm/docker (16G tmpfs) which has plenty of space.
+    subprocess.run(  # nosec B603 B607
+        ["pkill", "-f", "dockerd"],
+        capture_output=True,
+        check=False,
+    )
+    time.sleep(2)
+
     # Reset DOCKER_HOST to host socket for local dockerd
     os.environ["DOCKER_HOST"] = f"unix://{DOCKER_SOCK}"