fix(portability): one python/python3 note + cross-shell guidance for bash-only labs

- M1: single prominent note that the command may be python3/pip3 (modern macOS,
  default Debian/Ubuntu); referenced rather than repeated.
- Cross-shell notes where bash-only commands appear: M1 mkdir -p, M12 rm -f,
  M16 bind-mount (braced ${PWD} + PowerShell note), M19 inspect-runner.sh gains a
  timeout/gtimeout/bash-native fallback so it doesn't hang on stock macOS.

Closes #31
Closes #32

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TfzV5QvtPDz8LJS3Pu5VLT

modules/16-containers-and-reproducible-environments/README.md

@@ -226,10 +226,14 @@ containerize and run the app you already have.
    image (that keeps it lean; see *Where it breaks*):
 
    ```bash
-   docker run --rm -v "$PWD":/app -w /app python:3.12-slim \
+   docker run --rm -v "${PWD}:/app" -w /app python:3.12-slim \
      python -m unittest
    ```
 
+   > **On Windows:** this step bind-mounts your code, so the host path matters. Run it from WSL (or
+   > Git Bash), or from PowerShell — `${PWD}` resolves correctly in each. The other `docker run`
+   > commands mount nothing of yours and are identical everywhere.
+
    This is, in miniature, exactly what containerized CI does. If it passes here, it passes the same
    way on any machine with the engine — your laptop's local Python version is now irrelevant.