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/unit/test_cli_start_format.py

@@ -38,6 +38,7 @@ class TestStartFormatFlag(unittest.TestCase):
                 env=env,
                 capture_output=True,
                 text=True,
+                check=False,
             )
             self.assertNotEqual(0, result.returncode)
             self.assertIn(