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

docker-compose.yml

@@ -2,4 +2,9 @@ services:
   prayer:
     build: .
     ports:
-      - "3000:80"
+      - "3000:4000"
+    volumes:
+      - prayer-data:/data
+
+volumes:
+  prayer-data: