feat(py): step 1 — simple reachability checker (simple.py)

- python/simple.py: reads a plain-text site list (one URL/line, # comments),
  issues a GET per site, prints aligned OK/FAIL + elapsed ms, exits 0/1
- Config format forward-compatible with future key=value annotations
- HTTPError caught separately from URLError so HTTP status code appears in
  the FAIL message (e.g. "HTTP Error 404: Not Found")
- python/sites.txt: committed example config
- Makefile: PYTHON/PY_DIR/SITES vars; py-simple-run, py-phases-run, py-run,
  py-test, py-check, py-clean targets; umbrella test/check/clean include Python
- docs/plans/2026-07-01-10-39-py-simple.md: design plan
- docs/usage/py-simple.md: flags, format, examples, limitations

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

docs/plans/2026-07-01-10-39-py-simple.md

@@ -0,0 +1,47 @@
+# Python Port — Step 1: `simple.py`
+
+## Goal
+
+The simplest possible latency-checking script: read a plain-text list of sites,
+issue a GET to each, report whether it was reachable and how long it took.
+No phase breakdown, no flags beyond the config-file path. ~50 lines.
+
+## Input
+
+`python simple.py [sites.txt]`
+
+- Positional argument: path to the plain-text config (default: `sites.txt` in cwd).
+- Config format: one URL per line; `#` introduces a comment; blank lines ignored.
+  Forward-compatible with trailing `key=value` tokens that future steps may add
+  (the parser strips everything after the first whitespace token when reading the URL).
+
+## Output
+
+One line per site, aligned in three columns:
+
+```
+OK     147.11 ms  https://example.com
+FAIL   (connection refused)  http://localhost:8080
+FAIL   (name or service not known)  https://nonexistent.invalid
+```
+
+- `OK` / `FAIL` tag (7 chars padded), ms formatted as `%.2f ms`, then URL.
+- All output goes to `stdout`.
+- Exit `0` if every site returned a response (any HTTP status); `1` if any failed.
+
+## Implementation
+
+- `urllib.request.urlopen(url, timeout=10)` wrapped in a try/except.
+- Timing: `time.perf_counter()` bracketed around `urlopen` + `resp.read()` (drain
+  body so the number is real wall-clock including transfer).
+- Catch `urllib.error.URLError` and `Exception` for any network failure; extract
+  the reason string for the FAIL message.
+- Stdlib only: `urllib.request`, `urllib.error`, `time`, `sys`.
+
+## Files
+
+- `python/simple.py` — the script
+- `python/sites.txt` — example config (committed as a sample)
+- `docs/usage/py-simple.md` — user-facing doc
+- Makefile `py-simple-run` and `py-test` (empty stub) targets, wired into umbrella `test`
+- CHANGELOG.md entry