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/Stepper.tsx

@@ -0,0 +1,45 @@
+type StepState = 'idle' | 'active' | 'done';
+
+interface Step {
+  label: string;
+  state: StepState;
+}
+
+interface StepperProps {
+  steps: Step[];
+}
+
+function StepMarker({ state, index }: { state: StepState; index: number }) {
+  if (state === 'done') {
+    return (
+      <span className="stepper-marker" aria-hidden="true">
+        ✓
+      </span>
+    );
+  }
+  return (
+    <span className="stepper-marker" aria-hidden="true">
+      {index + 1}
+    </span>
+  );
+}
+
+export function Stepper({ steps }: StepperProps) {
+  return (
+    <div className="stepper" role="list">
+      {steps.map((step, index) => {
+        const isLast = index === steps.length - 1;
+        const nextStepDone = !isLast && steps[index].state === 'done';
+        return (
+          <div key={step.label} className="contents">
+            <div className="stepper-step" role="listitem" data-state={step.state}>
+              <StepMarker state={step.state} index={index} />
+              <span className="stepper-label">{step.label}</span>
+            </div>
+            {!isLast ? <div className="stepper-bar" data-done={nextStepDone ? 'true' : 'false'} /> : null}
+          </div>
+        );
+      })}
+    </div>
+  );
+}