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/nani_expr.py

@@ -1,6 +1,6 @@
 """Parse Naninovel expressions into data, never Python/JavaScript source code."""
-import re
 import math
+import re
 
 TOKEN = re.compile(r'''\s*(?:(\d+(?:\.\d*)?(?:[eE][+-]?\d+)?|\.\d+)|([A-Za-z_]\w*)|("(?:\\.|[^"\\])*"|'(?:\\.|[^'\\])*')|(&&|\|\||==|!=|<>|<=|>=|<<|>>|[()+\-*/%<>=!~?:,&|^]))''')
 PRECEDENCE = {"or": 2, "||": 2, "and": 3, "&&": 3, "|": 4, "^": 5,