feat(py): step 1 refinement — error-path example configs for simple.py

- python/configs/: 7 purpose-built config files, one per error class:
  all-ok.txt, dns-failure.txt, connection-refused.txt, timeout.txt,
  tls-errors.txt (badssl.com), http-errors.txt (real 404 paths on stable
  hosts), mixed.txt (one of each, no timeout)
- python/configs/usage.md: runnable sh commands + expected output per config,
  plus quick-sweep and full-sweep loops; commands written for running from
  the python/ directory
- docs/custom-usage-examples.md: example 11 added (all failure classes at once)
- docs/usage/py-simple.md: added pointer to python/configs/ and corrected
  limitation note (4xx/5xx are FAIL, not OK)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

python/configs/all-ok.txt

@@ -0,0 +1,7 @@
+# All sites are expected to respond successfully.
+# Run: python3.14 python/simple.py python/configs/all-ok.txt
+# Expected exit code: 0
+
+https://example.com
+https://www.google.com
+https://www.iana.org