Effective config with source tracking, Dnsmasq page, and test harness

- Effective config: track value sources (ConfigValueSource, EffectiveConfigSources)
  and show readonly badges/tooltips for non-managed files. Multi-value options
  use ValueWithSource/PathWithSource for JSON. StatusClient uses camelCase
  serialization for reliable deserialization.
- Parsing: align with dnsmasq (conf-file/conf-dir order, suffix filter, case-
  sensitive keys). DnsmasqConfIncludeParser and DnsmasqConfigSetService build
  effective config and sources. New DnsmasqConfigSetServiceTests.
- UI: rename Overview/Home to Dnsmasq (page, nav, doc comments). Add
  EffectiveConfigOptionItem and EffectiveConfigMultiValueRow components.
  Dnsmasq.razor uses them; Hosts.razor shows addn-hosts with source. Encode
  server-derived strings in markup to avoid XSS.
- Home section namespace: Components.Home -> Components.Dnsmasq (LogsSection,
  StatusSection, _Imports).
- Test data: expand testdata (README, resolv.dnsmasq, hosts.extra, dnsmasq.d
  configs). dhcp.conf static IP aligned with testnet.
- agents.md: add agent instructions for test harness and conventions.

src/DnsmasqWebUI/Client/Http/StatusClient.cs

@@ -1,3 +1,4 @@
+using System.Text.Json;
 using DnsmasqWebUI.Client.Http.Abstractions;
 using DnsmasqWebUI.Models;
 using System.Net.Http.Json;
@@ -8,9 +9,16 @@ public sealed class StatusClient : IStatusClient
 {
     private readonly HttpClient _http;
 
+    /// <summary>Matches API serialization (camelCase) so nested EffectiveConfigSources and tuple (value, source) deserialize correctly.</summary>
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        PropertyNameCaseInsensitive = true
+    };
+
     public StatusClient(HttpClient http) => _http = http;
 
     public async Task<DnsmasqServiceStatus> GetStatusAsync(CancellationToken ct = default) =>
-        await _http.GetFromJsonAsync<DnsmasqServiceStatus>("api/status", ct)
+        await _http.GetFromJsonAsync<DnsmasqServiceStatus>("api/status", JsonOptions, ct)
             ?? throw new InvalidOperationException("Unexpected null from api/status.");
 }