chore: add CI, lint config, login rate limit and split large modules

- Rate-limit failed logins (8 per 15 min per IP or username, 429 + Retry-After)
- Add ruff/mypy config and GitHub Actions workflow (ruff, pytest, tsc, tests, build)
- Apply ruff autofixes (import order, pyupgrade)
- Extract rpy_helpers.py, engine-util.ts, TranslationParts.tsx and
  translation-types.ts from oversized modules
- Add dependency-free React UI tests
- Refresh README and ARCHITECTURE (Naninovel/Tomie, status and plans)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/mods.py

@@ -2,12 +2,12 @@
 import copy
 import difflib
 import json
-from uuid import uuid4, uuid5, NAMESPACE_URL
+from uuid import NAMESPACE_URL, uuid4, uuid5
 
 from app.blobs import BLOB_ID_RE
-from app.pgvn import expression, statements
 from app.converter.locales import walk
 from app.converter.pipeline import anchors
+from app.pgvn import expression, statements
 from app.translation import file_json, put_json
 
 OPS = set("label camera say scene show hide with play stop queue voice pause menu if while jump call return exec window noop nvl".split())