chore: start transition layout — python into version-python/, scaffold version-rust/

- git mv of all existing files into version-python/ (history preserved)
- version-rust/: minimal cargo scaffold (edition 2024), no deps yet
- root AGENTS.md documents the transition rules and artifact/schema contract
- main is untouched; the python layout there stays as-is

.gitignore

@@ -1,24 +0,0 @@
-# Python
-__pycache__/
-*.pyc
-.venv/
-*.egg-info/
-
-# Run outputs (if OUT_DIR points into the repo)
-thread/
-downloads/
-export.json
-export.html
-state.json
-state.json.tmp
-failed_urls.txt
-manifest.jsonl
-*.log
-
-# Never commit credentials
-*.token
-.env
-
-# Algolia credentials (search-only key, still never commit)
-algolia.json
-gwshop_raw.json