refactor: flatten the crate to the repo root and drop the python version

The Rust rewrite has replaced the original python implementation, so the transition layout is no longer needed:

- move version-rust/{Cargo.toml,Cargo.lock,README.md,.gitignore,src,data} to the repo root; the crate is now the repo.
- move docs/SORTING.md and data/gwshop_catalog.json to the root.
- remove version-python/ entirely, plus the dev-only version-rust/tools/dump_warhammer_data.py (its only job was regenerating data/warhammer_data.json from python).
- rewrite AGENTS.md and README.md for the single-project layout; strip all version-python/version-rust references from code comments.
- fix the gwshop credential lookup: algolia.json now sits at CARGO_MANIFEST_DIR (crate root == repo root), not its parent.
- restore the credentials/run-output ignores in .gitignore (algolia.json, .env, *.token, downloads/, state.json, manifest.jsonl, ...).
- docs/SORTING.md: retarget the extraction/sorter/dlp examples at the dlphelper binary instead of the deleted python scripts.

cargo test: 86/86 green.

.gitignore

@@ -0,0 +1,21 @@
+/target
+
+# Algolia credentials (search-only key, still never commit)
+algolia.json
+gwshop_raw.json
+
+# Never commit credentials
+*.token
+.env
+
+# Run outputs (if OUT_DIR points into the repo)
+thread/
+downloads/
+extracted/
+export.json
+export.html
+state.json
+state.json.tmp
+failed_urls.txt
+manifest.jsonl
+*.log