Restore lost Russian dictionary sources from scrabble-solver history

The dict pipeline was moved out of scrabble-solver (256999b) into this repo,
but the initial import (d04470b) dropped three primary sources, and the
"Tidy sources" reorg (dd61ff1) git-ignored them while tools/README.md still
documented them as the committed source of truth — so the word-provenance
analysis could no longer run.

Recover them byte-identically from scrabble-solver's history (reachable from
its v1.0.0 tag):

- tools/orfo_dict_2025.pdf                 primary source (RAS orthographic dictionary PDF)
- sources/scrabble_ru/orfo_dict_2025.txt   pdftotext output, pipeline source of truth
- sources/scrabble_ru/all.txt              Stage-1 base, input to Stage 2

Stop ignoring them in .gitignore and fix the contradictory note in
sources/scrabble_ru/README.md (only the debug dumps are regenerated locally).

sources/scrabble_ru/README.md

@@ -5,5 +5,6 @@ pipeline under [`../../tools/`](../../tools/README.md) from the Russian academic
 dictionary, cross-checked against OpenCorpora and libmorph. `manual_confirm.txt` holds the
 hand-reviewed additions the pipeline merges in. Built to `dawg/ru_scrabble.dawg` (`make dawg-ru`).
 
-The pipeline's uncommitted intermediates (`orfo_dict_2025.txt`, `all.txt`, debug dumps) are
-regenerated here locally and are git-ignored.
+The pdftotext source of truth (`orfo_dict_2025.txt`) and the Stage-1 base (`all.txt`) are
+committed here; only the debug dumps (`undefined.txt`, `adjectives.txt`, `verbs.txt`,
+`singulars.txt`, `fate.tsv`) are regenerated locally and git-ignored.