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>

frontend/src/player/engine.ts

@@ -1,35 +1,17 @@
 // PGVN interpreter + in-game UI.
 
-import { AudioSystem, type Volumes } from "./audio";
+import { AudioSystem } from "./audio";
 import { JumpSignal, PyDict, Python, decodeValue, encodeValue, pyStr, truthy, type Scope } from "./python";
 import { Renderer, type ResolvedImage } from "./renderer";
 import { fastPoint, interpolate, parseText, plainText, renderText, waitPoints } from "./text";
 import { languageName, rememberLanguage, type Translator } from "./i18n";
 import { naniText } from "./naninovel";
+import { DEFAULT_SETTINGS, SLOTS, Restart, el, loadJSON, saveJSON, type SaveApi, type SaveMeta, type Settings } from "./engine-util";
 import type {
   CharacterDef, Expr, Frame, GameData, ImageDef, Label, Layer, Manifest, Node, SaveData, ScriptModule,
 } from "./types";
 
-export interface SaveMeta {
-  slot: string;
-  title: string;
-  updated_at: string;
-}
-
-export interface SaveApi<T = SaveData> {
-  list(): Promise<SaveMeta[]>;
-  get(slot: string): Promise<T | null>;
-  put(slot: string, title: string, data: T): Promise<void>;
-  remove(slot: string): Promise<void>;
-}
-
-interface Settings extends Volumes {
-  cps: number; // characters per second, 0 = instant
-  autoDelay: number; // seconds per 20 characters in auto mode
-}
-
-const DEFAULT_SETTINGS: Settings = { cps: 45, autoDelay: 1.2, music: 0.7, sound: 0.8, voice: 1 };
-const SLOTS = 12;
+export type { SaveApi, SaveMeta } from "./engine-util";
 
 interface LabelRef {
   label: Label;
@@ -37,32 +19,6 @@ interface LabelRef {
   index: number;
 }
 
-class Restart extends Error {}
-
-function el<K extends keyof HTMLElementTagNameMap>(tag: K, cls = "", text = ""): HTMLElementTagNameMap[K] {
-  const e = document.createElement(tag);
-  if (cls) e.className = cls;
-  if (text) e.textContent = text;
-  return e;
-}
-
-function loadJSON<T>(key: string, fallback: T): T {
-  try {
-    const raw = localStorage.getItem(key);
-    return raw ? { ...fallback, ...JSON.parse(raw) } : fallback;
-  } catch {
-    return fallback;
-  }
-}
-
-function saveJSON(key: string, value: unknown) {
-  try {
-    localStorage.setItem(key, JSON.stringify(value));
-  } catch {
-    /* storage unavailable */
-  }
-}
-
 export class Engine {
   private labels = new Map<string, LabelRef>();
   private anchors = new Map<string, { label: string; path: number[]; params?: [string, Expr | null][] | null }>();