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/converter/tomie_profile.py

@@ -1,7 +1,7 @@
 """Version-pinned Tomie metadata. Reads IL constants; never executes managed code."""
 import hashlib
-from pathlib import Path
 import re
+from pathlib import Path
 
 PROFILE = "tomie/expansion-1.3801"
 ASSEMBLY_HASH = "1c6aec12894362f1b9c62858a5a4c286eb93aee175ed1ef339218dc5a7b2729b"
@@ -110,8 +110,9 @@ def runtime_data(package) -> dict:
 
 def validate_expressions(scripts: dict) -> dict:
     """Check the full recovered expression corpus, including dynamic templates."""
-    from app.converter.nani_expr import assignment, parse
     from collections import Counter
+
+    from app.converter.nani_expr import assignment, parse
     expressions, errors = {}, Counter()
     examples = {}