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/pipeline.py

@@ -15,12 +15,18 @@ from app.blobs import put_bytes, put_file
 from app.config import get_settings
 from app.converter import assets, locales
 from app.converter.archive import extract, find_game_dir
+from app.converter.compatibility import (
+    CompatibilityError,
+    Issue,
+    audit_ir,
+    detect,
+    require_supported_scripts,
+)
 from app.converter.rpa import RpaError, extract_rpa
 from app.converter.rpy_lexer import ParseError
 from app.converter.rpy_parser import RpyParser, ScriptData
 from app.converter.rpyc import decompile_missing
 from app.converter.source import read_source
-from app.converter.compatibility import CompatibilityError, Issue, audit_ir, detect, require_supported_scripts
 
 log = logging.getLogger(__name__)
 FORMAT = "pgvn/1"