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/hooks/useShareLink.js

@@ -0,0 +1,48 @@
+// Read-only share link for the open project: status, enable, revoke, copy.
+import { useEffect, useState } from 'react';
+import { disableSharing, enableSharing, getShareStatus } from '../syncService.js';
+
+export function useShareLink(projectId) {
+  const [shareToken, setShareToken] = useState(null);
+  const [shareBusy, setShareBusy] = useState(false);
+  const [shareCopied, setShareCopied] = useState(false);
+
+  useEffect(() => {
+    setShareToken(null);
+    if (!projectId) return;
+    let active = true;
+    getShareStatus(projectId).then((result) => {
+      if (active && result.ok) setShareToken(result.data.shareToken);
+    });
+    return () => { active = false; };
+  }, [projectId]);
+
+  const shareUrl = shareToken
+    ? `${window.location.origin}${window.location.pathname}?share=${shareToken}`
+    : '';
+
+  const enable = async () => {
+    setShareBusy(true);
+    const result = await enableSharing(projectId);
+    setShareBusy(false);
+    if (result.ok) setShareToken(result.data.shareToken);
+  };
+
+  const revoke = async () => {
+    if (!window.confirm('Revoke this share link? Anyone using it will lose access immediately.')) return;
+    setShareBusy(true);
+    const result = await disableSharing(projectId);
+    setShareBusy(false);
+    if (result.ok) setShareToken(null);
+  };
+
+  const copy = () => {
+    if (!shareUrl) return;
+    navigator.clipboard.writeText(shareUrl).then(() => {
+      setShareCopied(true);
+      window.setTimeout(() => setShareCopied(false), 2000);
+    });
+  };
+
+  return { shareToken, shareUrl, shareBusy, shareCopied, enable, revoke, copy };
+}

src/hooks/useSharedView.js

@@ -0,0 +1,20 @@
+// A ?share=TOKEN URL shows a read-only view of someone else's project. No
+// login is needed, so this runs independently of auth.
+import { useEffect, useState } from 'react';
+import { getSharedProject } from '../syncService.js';
+
+export function useSharedView() {
+  const [token] = useState(() => new URLSearchParams(window.location.search).get('share'));
+  const [project, setProject] = useState(null);
+  const [error, setError] = useState('');
+
+  useEffect(() => {
+    if (!token) return;
+    getSharedProject(token).then((result) => {
+      if (result.ok) setProject(result.data);
+      else setError(result.error ?? 'This share link is invalid or has been revoked.');
+    });
+  }, [token]);
+
+  return { token, project, error };
+}