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

testdata/README

@@ -17,6 +17,6 @@ Source for the Docker test harness: `scripts/prepare-test-mount.sh` syncs this d
 | **hosts** | First addn-hosts file; system hosts when `Dnsmasq:SystemHostsPath` points here. |
 | **hosts.extra** | Second addn-hosts file. |
 | **resolv.dnsmasq** | Minimal file for resolv-file= in 03-more.conf; must exist so dnsmasq does not fail/warn. |
-| **leases** | Sample DHCP leases for harness leases table. |
+| **leases** | Sample DHCP leases for unit tests only; not synced to the harness. The harness uses the path from config (`dhcp-leasefile=` in dnsmasq-test.conf); the app discovers and monitors that file; dnsmasq creates it when DHCP clients obtain addresses. |
 
 Harness usage (start/stop/tidy): see **agents.md** in the repo root.