Add DOCX export endpoint and Export button

- GET /api/export generates a Word document with all non-archived prayers
- Accepts ?status=active|answered|all and ?tag= query params to match
  the current filter/tag selection in the UI
- Document sections: Active Prayers + Answered Prayers with page break,
  each prayer showing person, request, answer, dates, and tags
- Styled with Palatino Linotype, page numbers in footer
- Export button in the toolbar triggers download of dated .docx file

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DReRqHxSYuVfCzTzQGD9hZ

src/App.css

@@ -214,6 +214,22 @@ body {
   gap: .5rem;
 }
 
+.btn-export {
+  background: var(--surface);
+  border-color: var(--border);
+  color: var(--text-muted);
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+  font-size: .82rem;
+  padding: .38rem .8rem;
+  white-space: nowrap;
+  flex-shrink: 0;
+}
+
+.btn-export:hover {
+  color: var(--text);
+  border-color: var(--primary);
+}
+
 /* Search */
 .search-wrap {
   position: relative;