Persist prayer data to a mounted Docker volume via Express API

Replaces localStorage with a JSON-file backend (server.js). Prayers are
stored in /data/prayers.json, which is mounted as a named Docker volume so
data survives container restarts and rebuilds. React fetches from /api/prayers.

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

src/App.css

@@ -234,6 +234,13 @@ body {
   gap: 0.75rem;
 }
 
+.loading {
+  text-align: center;
+  color: var(--text-muted);
+  font-style: italic;
+  padding: 1rem 0;
+}
+
 .empty {
   text-align: center;
   color: var(--text-muted);