Dnsmasq/Hosts UI tweaks, test harness: down before redeploy, exclude leases from mount

- Dnsmasq page: Config (Main config, Managed file, Config set) under Service configuration; remove Paths/Leases (in Effective config DHCP); EffectiveConfigSection collapsible groups; StatusSection flex-wrap
- Hosts: HostsFileSection always shows table; 'No host entries' in tbody when empty
- Models: reorganize into sub-namespaces (Config, EffectiveConfig, Hosts, Dhcp, Status); move EffectiveConfig/Status/Logs components under Dnsmasq
- Test harness: prepare-test-mount.sh runs 'docker compose down' before mount+up so all containers (including DHCP clients) restart; exclude testdata/leases from sync (unit tests only); testdata/README

docker-compose.test.yml

@@ -21,7 +21,6 @@ services:
       DNSMASQ_CONF: /data/dnsmasq-test.conf
       Dnsmasq__MainConfigPath: /data/dnsmasq-test.conf
       Dnsmasq__ManagedFileName: zz-dnsmasq-webui.conf
-      # System hosts: app default /etc/hosts shows the container's hosts file (read-only).
       Dnsmasq__ReloadCommand: "pkill -HUP -x dnsmasq"
       Dnsmasq__StatusCommand: "pgrep -x dnsmasq"
       # Simulated systemctl status + real logs (dnsmasq logs to /data/dnsmasq.log via log-facility in dnsmasq-test.conf)