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/DropZone.tsx

@@ -0,0 +1,88 @@
+import { useState, type ChangeEvent, type DragEvent, type MouseEvent } from 'react';
+import { formatFileSize } from '../lib/ids';
+
+interface DropZoneProps {
+  file: File | null;
+  onFileChange: (file: File | null) => void;
+  accept?: string;
+}
+
+export function DropZone({ file, onFileChange, accept = '.ipa,application/octet-stream' }: DropZoneProps) {
+  const [isDragOver, setIsDragOver] = useState(false);
+
+  const handleDragOver = (event: DragEvent<HTMLLabelElement>) => {
+    event.preventDefault();
+    setIsDragOver(true);
+  };
+
+  const handleDragLeave = () => {
+    setIsDragOver(false);
+  };
+
+  const handleDrop = (event: DragEvent<HTMLLabelElement>) => {
+    event.preventDefault();
+    setIsDragOver(false);
+    const dropped = event.dataTransfer?.files?.[0] ?? null;
+    if (dropped) onFileChange(dropped);
+  };
+
+  const handleInputChange = (event: ChangeEvent<HTMLInputElement>) => {
+    const selected = event.target.files?.[0] ?? null;
+    onFileChange(selected);
+  };
+
+  const handleClear = (event: MouseEvent<HTMLButtonElement>) => {
+    event.preventDefault();
+    onFileChange(null);
+  };
+
+  return (
+    <div>
+      <label
+        className={`drop-zone${isDragOver ? ' dragover' : ''}`}
+        onDragEnter={handleDragOver}
+        onDragOver={handleDragOver}
+        onDragLeave={handleDragLeave}
+        onDrop={handleDrop}
+      >
+        <svg
+          className="mx-auto mb-2 h-7 w-7 text-subtle"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          strokeWidth="1.5"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          aria-hidden="true"
+        >
+          <path d="M14 3v4a1 1 0 0 0 1 1h4" />
+          <path d="M17 21H7a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h7l5 5v11a2 2 0 0 1-2 2z" />
+          <path d="M12 11v6m-3-3 3 3 3-3" />
+        </svg>
+
+        {file ? (
+          <>
+            <span className="block truncate text-[14px] font-medium text-ink">{file.name}</span>
+            <span className="mt-1 block text-[12px] text-muted">
+              {formatFileSize(file.size)}
+              <button
+                type="button"
+                onClick={handleClear}
+                className="ml-2 text-[var(--color-accent)] underline-offset-2 hover:underline"
+              >
+                Clear
+              </button>
+            </span>
+          </>
+        ) : (
+          <>
+            <span className="block text-[14px] font-medium text-ink">No file selected</span>
+            <span className="mt-1 block text-[12px] text-muted">Click or drag .ipa here</span>
+          </>
+        )}
+
+        <input type="file" accept={accept} className="hidden" onChange={handleInputChange} value="" />
+      </label>
+    </div>
+  );
+}