style: pass explicit check= to every subprocess.run call

Silences pylint W1510 / ruff PLW1510 across the codebase. The choice
at each site reflects existing intent:

- check=True where the caller implicitly trusts success (docker ps /
  network ls returning stdout, docker build, exec chown/chmod inside
  provisioners).
- check=False where the caller inspects .returncode (race-retry on
  docker run, pipelock sidecar lifecycle, network plumbing, exec_claude
  propagating the session's exit code, best-effort cleanup paths).

No behavior change; check= defaults to False so the False sites are
semantically identical.

tests/_docker.py

@@ -15,6 +15,7 @@ def docker_available() -> bool:
             ["docker", "info"],
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
+            check=False,
         ).returncode
         == 0
     )