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/analyze.py

@@ -12,12 +12,12 @@ import sys
 import tempfile
 import time
 from collections import Counter
+from dataclasses import asdict
 from pathlib import Path
 
 from app.converter import assets, locales
-from app.converter.compatibility import Issue, audit_ir
-from dataclasses import asdict
 from app.converter.archive import ArchiveError, find_game_dir
+from app.converter.compatibility import Issue, audit_ir
 from app.converter.pipeline import _auto_images, _is_engine_file, _resolve_image, anchors
 from app.converter.rpa import RpaError, extract_rpa, read_index
 from app.converter.rpy_lexer import ParseError