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/Field.test.tsx

@@ -0,0 +1,36 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { describe, expect, it, vi } from 'vitest';
+import { Field } from './Field';
+
+describe('Field', () => {
+  it('links the label to the input via htmlFor / id', () => {
+    render(<Field label="Email" />);
+    const input = screen.getByLabelText('Email');
+    expect(input).toBeInTheDocument();
+  });
+
+  it('forwards the provided id when given', () => {
+    render(<Field label="Email" id="my-email" />);
+    expect(screen.getByLabelText('Email')).toHaveAttribute('id', 'my-email');
+  });
+
+  it('renders a hint when no error is present', () => {
+    render(<Field label="N" hint="help text" />);
+    expect(screen.getByText('help text')).toBeInTheDocument();
+  });
+
+  it('renders the error instead of the hint and marks aria-invalid', () => {
+    render(<Field label="N" hint="ignored" error="bad" />);
+    expect(screen.queryByText('ignored')).not.toBeInTheDocument();
+    expect(screen.getByText('bad')).toBeInTheDocument();
+    expect(screen.getByLabelText('N')).toHaveAttribute('aria-invalid', 'true');
+  });
+
+  it('fires onChange when typing', async () => {
+    const onChange = vi.fn();
+    render(<Field label="N" onChange={onChange} defaultValue="" />);
+    await userEvent.type(screen.getByLabelText('N'), 'a');
+    expect(onChange).toHaveBeenCalled();
+  });
+});