Extract project header, share link, exports, and auth status

- ProjectHeader component replaces the headerButtons JSX in context; it
  owns the export menu and share panel state.
- useShareLink (share status/enable/revoke/copy) and useSharedView
  (?share= read-only view, now used directly by the router).
- utils/projectExport: HTML/Markdown/DOCX download and print-to-PDF.
- AuthStatus component replaces the authStatus JSX in context.
- Pages import wordStudy helpers directly instead of via context.
- Remove dead copyPronunciationGuide (PronunciationPage has its own).
- Tests: Markdown export, enabling a share link, the ?share= view.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/components/AuthStatus.jsx

@@ -0,0 +1,35 @@
+// Signed-in email plus Admin / Settings / Log out buttons for page headers.
+import { useApp } from '../context/AppContext.js';
+
+export default function AuthStatus() {
+  const { authUser, setCurrentPage, logout } = useApp();
+  if (!authUser) return null;
+  return (
+    <div className="flex items-center gap-2 text-sm text-slate-300">
+      <span className="hidden sm:inline">{authUser.email}</span>
+      {authUser.isAdmin && (
+        <button
+          type="button"
+          onClick={() => setCurrentPage('admin')}
+          className="rounded-xl border border-white/15 bg-white/10 px-3 py-1.5 text-xs text-white transition hover:bg-white/15"
+        >
+          🛡 Admin
+        </button>
+      )}
+      <button
+        type="button"
+        onClick={() => setCurrentPage('settings')}
+        className="rounded-xl border border-white/15 bg-white/10 px-3 py-1.5 text-xs text-white transition hover:bg-white/15"
+      >
+        ⚙ Settings
+      </button>
+      <button
+        type="button"
+        onClick={logout}
+        className="rounded-xl border border-white/15 bg-white/10 px-3 py-1.5 text-xs text-white transition hover:bg-white/15"
+      >
+        Log out
+      </button>
+    </div>
+  );
+}