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/TwoFactorModal.test.tsx

@@ -0,0 +1,58 @@
+import { fireEvent, render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { describe, expect, it, vi } from 'vitest';
+import { TwoFactorModal } from './TwoFactorModal';
+
+describe('TwoFactorModal', () => {
+  it('is hidden when closed', () => {
+    const { container } = render(<TwoFactorModal open={false} onSubmit={() => {}} onCancel={() => {}} />);
+    expect(container.querySelector('.modal')).not.toHaveClass('open');
+  });
+
+  it('focuses the input when opened', async () => {
+    render(<TwoFactorModal open onSubmit={() => {}} onCancel={() => {}} />);
+    // useEffect runs a setTimeout(0) before focusing — let it tick.
+    await new Promise((resolve) => setTimeout(resolve, 10));
+    expect(screen.getByLabelText('Verification Code')).toHaveFocus();
+  });
+
+  it('shows an inline error when submitting an empty code', async () => {
+    const onSubmit = vi.fn();
+    render(<TwoFactorModal open onSubmit={onSubmit} onCancel={() => {}} />);
+    await userEvent.click(screen.getByRole('button', { name: 'Verify' }));
+    expect(screen.getByText('Please enter verification code.')).toBeInTheDocument();
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
+  it('clears the error once the user starts typing', async () => {
+    render(<TwoFactorModal open onSubmit={() => {}} onCancel={() => {}} />);
+    await userEvent.click(screen.getByRole('button', { name: 'Verify' }));
+    expect(screen.getByText('Please enter verification code.')).toBeInTheDocument();
+    await userEvent.type(screen.getByLabelText('Verification Code'), '1');
+    expect(screen.queryByText('Please enter verification code.')).not.toBeInTheDocument();
+  });
+
+  it('submits a trimmed code on Enter', async () => {
+    const onSubmit = vi.fn();
+    render(<TwoFactorModal open onSubmit={onSubmit} onCancel={() => {}} />);
+    const input = screen.getByLabelText('Verification Code');
+    await userEvent.type(input, '  123456  ');
+    fireEvent.keyDown(input, { key: 'Enter' });
+    expect(onSubmit).toHaveBeenLastCalledWith('123456');
+  });
+
+  it('submits via the Verify button', async () => {
+    const onSubmit = vi.fn();
+    render(<TwoFactorModal open onSubmit={onSubmit} onCancel={() => {}} />);
+    await userEvent.type(screen.getByLabelText('Verification Code'), '654321');
+    await userEvent.click(screen.getByRole('button', { name: 'Verify' }));
+    expect(onSubmit).toHaveBeenLastCalledWith('654321');
+  });
+
+  it('calls onCancel when Cancel is clicked', async () => {
+    const onCancel = vi.fn();
+    render(<TwoFactorModal open onSubmit={() => {}} onCancel={onCancel} />);
+    await userEvent.click(screen.getByRole('button', { name: 'Cancel' }));
+    expect(onCancel).toHaveBeenCalledTimes(1);
+  });
+});