Fix editor full-screen and add parent-side doc viewer

Student editor:
- Add body.docs-editor-open class when editor opens; hide hero, nav,
  confetti so nothing bleeds behind the fixed overlay

Admin docs panel:
- New "Documents" sidebar entry listing all submitted docs with student
  name, date, and unread badge
- Click any doc to open it in OnlyOffice in view (read-only) mode
- Download button for offline access
- /api/docs/bykey/:key/editor-config server route for admin viewer

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.js

@@ -2546,6 +2546,20 @@ app.get('/api/docs/config', (req, res) => {
   res.json({ onlyofficeUrl: ONLYOFFICE_URL, serverUrl: SERVER_URL });
 });
 
+// Returns a fully-signed OnlyOffice editor config — lookup by doc key (for admin)
+app.get('/api/docs/bykey/:key/editor-config', (req, res) => {
+  const doc = db.prepare(`SELECT d.*, s.name AS student_name FROM documents d JOIN students s ON s.id = d.student_id WHERE d.doc_key = ?`).get(req.params.key);
+  if (!doc) return res.status(404).json({ error: 'Not found' });
+  const config = {
+    document: { fileType: 'docx', key: doc.doc_key, title: doc.title, url: `${SERVER_URL}/api/docs/file/${doc.filename}`, permissions: { edit: false, download: true, print: true } },
+    editorConfig: { user: { id: 'parent', name: 'Parent' }, mode: 'view', lang: 'en', customization: { logo: { visible: false }, compactHeader: true, toolbarNoTabs: true } },
+    type: 'desktop', height: '100%', width: '100%',
+  };
+  const token = jwtSign(config);
+  if (token) config.token = token;
+  res.json({ onlyofficeUrl: ONLYOFFICE_URL, config });
+});
+
 // Returns a fully-signed OnlyOffice editor config for a specific document
 app.get('/api/docs/:id/editor-config', (req, res) => {
   const doc = db.prepare(`SELECT d.*, s.name AS student_name FROM documents d JOIN students s ON s.id = d.student_id WHERE d.id = ?`).get(req.params.id);