fix(demo): repair Kiwix service with catalog-based ZIM bootstrap

Kiwix was failing to start: its inline bootstrap command had a shell
syntax error (a YAML-wrapped multi-line wget left a dangling `||`), and
the hard-coded sample-ZIM URL returned 404 because Kiwix rotates the
date-stamped filenames monthly.

Replace the inline command with a bind-mounted bootstrap script that
resolves the current ZIM filename from the Kiwix OPDS catalog at startup,
so the download URL never rots. kiwix-serve is also started on port 8080
to match the container port mapping and healthcheck (it defaults to 80).

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

demo/docker-compose.yml.template

@@ -750,23 +750,11 @@ services:
       - "${KIWIX_PORT}:8080"
     volumes:
       - ${COMPOSE_PROJECT_NAME}_kiwix_data:/data
+      - ./config/kiwix/bootstrap.sh:/bootstrap.sh:ro
     entrypoint: []
     command:
-      - /bin/sh
-      - -c
-      - |
-        if ! ls /data/*.zim 1>/dev/null 2>&1; then
-          echo 'No ZIM files found. Downloading sample ZIM...';
-          wget -q -O /data/demo.zim
-            'https://download.kiwix.org/zim/other/bleedingedge_climate-change_en.zim'
-            || echo 'Download failed';
-        fi
-        if ls /data/*.zim 1>/dev/null 2>&1; then
-          exec kiwix-serve /data/*.zim
-        else
-          echo 'No ZIM files available, sleeping indefinitely'
-          exec sleep infinity
-        fi
+      - sh
+      - /bootstrap.sh
     environment:
       - PUID=${DEMO_UID}
       - PGID=${DEMO_GID}