stacks/miniflux: flatten to single network; fix verify

Initial deploy failed with 'Container cannot be connected to network
endpoints: miniflux-net, traefik-net' — the docker engine balks at
joining a brand-new internal network and an existing external
network in one create step.

Flattened both containers onto traefik-net only. The DB password
still protects miniflux-db, and traefik-net is internal-LAN-only,
so co-locating them is fine. Verify step updated to check for
traefik-net membership instead of the (now-gone) miniflux-net.

playbooks/deploy-miniflux.yaml

@@ -77,6 +77,6 @@ verify:
     shell: docker inspect miniflux-db --format '{{.State.Status}}' | grep -qE 'running|created|restarting'
     changed_when: "false"
 
-  - name: Both containers on miniflux-net
-    shell: docker inspect miniflux miniflux-db --format '{{json .NetworkSettings.Networks}}' | grep -q miniflux-net
+  - name: Both containers on traefik-net
+    shell: docker inspect miniflux miniflux-db --format '{{json .NetworkSettings.Networks}}' | grep -q traefik-net
     changed_when: "false"