refactor: migrate frontend to React + Tailwind, add Docker + tests

Replace the vanilla-TS innerHTML frontend with a type-checked React
component tree (React 19 + Tailwind v4 + Vite).

Frontend:
- 14 components: Header, Stepper, LoginPage, LoginModal, SignPage,
  DropZone, DevicePicker, ProgressCard, SavedAccountsList, TrustModal,
  TwoFactorModal, Button, Field, Chip, Modal
- lib/ extracts: storage (10 localStorage keys preserved), pair-record,
  account-session, log-parser, ids, use-log hook
- flows/ encapsulate async pair/login/sign/install with dependency injection
- Accounts page as main view with Add Account modal
- Fullscreen progress overlay during sign/install
- Account selector + device picker on Sign page
- Security notice in login modal (server trust warning)
- All addLog calls mirrored to console.log for devtools debugging

Build:
- bun run dev: submodule init + install + wasm dist + vite + wrangler
- bun run setup: one-shot project bootstrap
- Docker: multi-stage bun build → nginx on :3000
- build:wasm:dist copies pre-built src→dist (no Rust/Emscripten needed)
- jszip/node-forge/fflate pre-bundled for CJS→ESM conversion

Tests:
- 163 vitest tests (happy-dom): all lib, components, App integration,
  WASM dist artifact checks, libcurl Apple connectivity, anisette init
  error handling

Cleanup:
- Delete yarn.lock (bun.lock canonical), expand .gitignore
- Remove README.zh.md, rewrite README.md + AGENTS.md
- Update libcurl.js submodule to f65d440 (CI build artifacts)

frontend/src/components/ui/Modal.tsx

@@ -0,0 +1,46 @@
+import { useEffect, type ReactNode } from 'react';
+
+interface ModalProps {
+  open: boolean;
+  onClose?: () => void;
+  labelledBy: string;
+  children: ReactNode;
+  closeOnBackdrop?: boolean;
+  closeOnEscape?: boolean;
+}
+
+export function Modal({
+  open,
+  onClose,
+  labelledBy,
+  children,
+  closeOnBackdrop = false,
+  closeOnEscape = true,
+}: ModalProps) {
+  useEffect(() => {
+    if (!open || !closeOnEscape || !onClose) return;
+    const handler = (event: KeyboardEvent) => {
+      if (event.key === 'Escape') {
+        event.preventDefault();
+        onClose();
+      }
+    };
+    window.addEventListener('keydown', handler);
+    return () => window.removeEventListener('keydown', handler);
+  }, [open, closeOnEscape, onClose]);
+
+  return (
+    <div
+      className={`modal${open ? ' open' : ''}`}
+      aria-hidden={open ? 'false' : 'true'}
+      onClick={(event) => {
+        if (!closeOnBackdrop || !onClose) return;
+        if (event.target === event.currentTarget) onClose();
+      }}
+    >
+      <section role="dialog" aria-modal="true" aria-labelledby={labelledBy} className="modal-panel">
+        {children}
+      </section>
+    </div>
+  );
+}