Add Unraid deployment setup

docker-compose.unraid.yml bind-mounts data to /mnt/user/appdata/kids-calendar
instead of a named volume, matching Unraid's appdata convention so backup
plugins pick it up. UNRAID.md covers getting the code onto the array,
running via Compose Manager or terminal, reverse-proxy/HTTPS notes, and
updating. Linked from README.

docker-compose.unraid.yml

@@ -0,0 +1,16 @@
+services:
+  kids-calendar:
+    build: .
+    container_name: kids-calendar
+    ports:
+      - "3007:3007"
+    volumes:
+      # Unraid convention: bind-mount to /mnt/user/appdata so it shows up
+      # in the Docker tab, gets picked up by appdata backup plugins, etc.
+      # Create this folder before first run (see UNRAID.md).
+      - /mnt/user/appdata/kids-calendar:/app/data
+    environment:
+      - SESSION_SECRET=${SESSION_SECRET:?set a long random value in .env}
+      - COOKIE_SECURE=${COOKIE_SECURE:-false}
+      - DISABLE_PUBLIC_SIGNUP=${DISABLE_PUBLIC_SIGNUP:-false}
+    restart: unless-stopped