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/tests/test_compatibility.py

@@ -1,13 +1,17 @@
 import asyncio
 import json
-from pathlib import Path
-from types import SimpleNamespace
 import zipfile
+from types import SimpleNamespace
 
 import pytest
 
 from app.config import get_settings
-from app.converter.compatibility import CompatibilityError, audit_ir, detect, require_supported_scripts
+from app.converter.compatibility import (
+    CompatibilityError,
+    audit_ir,
+    detect,
+    require_supported_scripts,
+)
 from app.converter.nani_compiler import compile_package
 from app.converter.nani_expr import assignment, parse
 from app.converter.nani_package import Package, decode_script, text_records
@@ -92,8 +96,8 @@ def test_renpy_atl_animation_is_rejected_instead_of_becoming_static():
 
 
 def test_source_encoding_is_preserved_or_explicitly_rejected(tmp_path):
-    from app.converter.source import read_source
     from app.converter.rpy_lexer import ParseError
+    from app.converter.source import read_source
     source = tmp_path / "script.rpy"
     source.write_bytes('# coding: cp1251\nlabel start:\n    "Привет"'.encode("cp1251"))
     assert "Привет" in read_source(source)
@@ -222,8 +226,8 @@ def test_naninovel_resources_keep_keys_delimiters_and_context():
 def test_naninovel_import_localization_and_mod_editor_roundtrip(tmp_path, monkeypatch):
     from app.blobs import read_bytes
     from app.converter.naninovel import convert_naninovel
-    from app.translation import apply_changes, locale_tables, text_index
     from app.mods import document, validate
+    from app.translation import apply_changes, locale_tables, text_index
 
     monkeypatch.setenv("DATA_DIR", str(tmp_path / "library"))
     get_settings.cache_clear()
@@ -250,6 +254,7 @@ def test_naninovel_import_localization_and_mod_editor_roundtrip(tmp_path, monkey
 
 def test_unity_codec_restores_global_hooks_after_error():
     from UnityPy.helpers import TypeTreeHelper as helper
+
     from app.converter.unity_scripts import ScriptCodec
     codec = ScriptCodec.__new__(ScriptCodec)
     before = (helper.read_value, helper.write_value, helper.read_typetree_boost, helper.get_ref_type_node)
@@ -288,9 +293,10 @@ def test_unused_renpy_translation_entries_are_not_script_blockers(tmp_path):
 
 
 def test_upload_rejects_unsupported_engine_without_queueing(tmp_path, monkeypatch):
+    from fastapi import HTTPException
+
     from app.routers import versions
     from app.uploads import upload_path
-    from fastapi import HTTPException
 
     source = tmp_path / "unsupported.zip"
     with zipfile.ZipFile(source, "w") as archive: