Tidy sources into sources/<variant>/ + tools/

Consolidate the scattered build inputs (dictionaries/english/, dictprep/russian/)
into one sources/ tree keyed by the variant labels (scrabble_en/scrabble_ru/
erudit_ru), and move the Russian prep pipeline to tools/. The dawg outputs and
their filenames are unchanged — rebuilt byte-identical (en_sowpods/ru_scrabble/
ru_erudit) — so the release artifact and the backend are unaffected.

ru_stage2.py OUT_DIR and the ruwords flag defaults are repointed to
sources/scrabble_ru/; Makefile / CI / cmd/builddict default / README updated;
pipeline intermediates git-ignored. Verified: make dawg byte-identical to the
committed baseline, py_compile + go vet of the moved tools. The full Russian
regeneration pipeline (pymorphy3/libmorph/orfo PDF) was not run here.

README.md

@@ -17,9 +17,9 @@ byte-identical to the solver's committed test fixtures.
 
 | file | variant | source |
 | --- | --- | --- |
-| `en_sowpods.dawg` | English (SOWPODS) | `dictionaries/english/sowpods.txt` |
-| `ru_scrabble.dawg` | Russian Scrabble | `dictprep/russian/scrabble.txt` |
-| `ru_erudit.dawg` | Эрудит | `dictprep/russian/erudit.txt` (Ё→Е folded `scrabble.txt`, via `dictprep/fold_yo.py`) |
+| `en_sowpods.dawg` | English (SOWPODS) | `sources/scrabble_en/sowpods.txt` |
+| `ru_scrabble.dawg` | Russian Scrabble | `sources/scrabble_ru/scrabble.txt` |
+| `ru_erudit.dawg` | Эрудит | `sources/erudit_ru/erudit.txt` (Ё→Е folded `scrabble.txt`, via `tools/fold_yo.py`) |
 
 The CI (`.gitea/workflows/build.yaml`) rebuilds them on every push/PR as a validation gate
 (inlined `go run`, no `make`/`python` needed on the runner). Release artifacts are published per
@@ -30,11 +30,11 @@ a new release, never breaking a running backend).
 
 ## Sources / provenance
 
-- **English:** `dictionaries/english/sowpods.txt`, vendored from
+- **English:** `sources/scrabble_en/sowpods.txt`, vendored from
   [`kamilmielnik/scrabble-dictionaries`](https://github.com/kamilmielnik/scrabble-dictionaries).
-- **Russian:** `dictprep/russian/scrabble.txt`, derived from the Russian academic orthographic
-  dictionary by the tooling under `dictprep/` (see `dictprep/README.md`); `dictprep/russian/erudit.txt`
-  is its Ё→Е folded form (`dictprep/fold_yo.py`). Only the prepared word lists are vendored; the
+- **Russian:** `sources/scrabble_ru/scrabble.txt`, derived from the Russian academic orthographic
+  dictionary by the tooling under `tools/` (see `tools/README.md`); `sources/erudit_ru/erudit.txt`
+  is its Ё→Е folded form (`tools/fold_yo.py`). Only the prepared word lists are vendored; the
   heavy upstream source (the orfo PDF/text) is not.
 
 ## Build
@@ -45,7 +45,7 @@ make dawg     # -> dawg/{en_sowpods,ru_scrabble,ru_erudit}.dawg
 
 Requires Go (module deps fetched with `GOPRIVATE=gitea.iliadenisov.ru/*`, exported by the
 Makefile). No `python` is needed for the build — the Ё→Е fold is committed as `erudit.txt`;
-regenerate it with `python3 dictprep/fold_yo.py dictprep/russian/scrabble.txt > dictprep/russian/erudit.txt`.
+regenerate it with `python3 tools/fold_yo.py sources/scrabble_ru/scrabble.txt > sources/erudit_ru/erudit.txt`.
 
 ## Release