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

src/DnsmasqWebUI/Components/EffectiveConfig/EffectiveConfigMultiValueRow.razor

@@ -1,10 +0,0 @@
-@namespace DnsmasqWebUI.Components.EffectiveConfig
-
-<li>
-    <strong>@Label:</strong> @Content
-</li>
-
-@code {
-    [Parameter] public string Label { get; set; } = "";
-    [Parameter] public MarkupString Content { get; set; }
-}

src/DnsmasqWebUI/Components/EffectiveConfig/EffectiveConfigOptionItem.razor

@@ -1,15 +0,0 @@
-@namespace DnsmasqWebUI.Components.EffectiveConfig
-
-<li title="@(Source?.GetReadOnlyTooltip())">
-    <strong>@Label:</strong> @DisplayValue
-    @if (Source?.IsReadOnly == true)
-    {
-        <span class="badge bg-secondary ms-1">readonly</span>
-    }
-</li>
-
-@code {
-    [Parameter] public string Label { get; set; } = "";
-    [Parameter] public string DisplayValue { get; set; } = "";
-    [Parameter] public ConfigValueSource? Source { get; set; }
-}