Refactor: reorganise namespaces and move service DTOs to Models/Contracts

- Move Client/Http, Services, Parsers under Infrastructure/ (Client, Services, Parsers)
- Move config helpers (DnsmasqConfKeys, DnsmasqOptionTooltips, DnsmasqFileEncoding, EffectiveConfigFieldBuilder) to Infrastructure/Helpers/Config; ApiJsonOptions to Helpers/Http
- Move Configuration types (ApplicationOptions, DnsmasqOptions, DnsmasqOptionsValidator) to Models/Config
- Merge Models/Status and Models/EffectiveConfig into Models/Dnsmasq and Models/Dnsmasq/EffectiveConfig
- Move Client/Models and Client/Services to Models/Client and Infrastructure/Services
- Move ConfigSetSnapshot, HostsSnapshot, ProcessRunResult, ManagedConfigContent from Infrastructure/Services/Abstractions to Models/Contracts
- Update all namespaces and usings; tests pass

src/DnsmasqWebUI/Infrastructure/Client/ReloadClient.cs

@@ -0,0 +1,21 @@
+using DnsmasqWebUI.Infrastructure.Client.Abstractions;
+using DnsmasqWebUI.Infrastructure.Helpers.Http;
+using DnsmasqWebUI.Infrastructure.Services.Abstractions;
+using System.Net.Http.Json;
+
+namespace DnsmasqWebUI.Infrastructure.Client;
+
+public sealed class ReloadClient : IReloadClient
+{
+    private readonly HttpClient _http;
+
+    public ReloadClient(HttpClient http) => _http = http;
+
+    public async Task<ReloadResult> ReloadAsync(CancellationToken ct = default)
+    {
+        var response = await _http.PostAsync("api/reload", null, ct);
+        response.EnsureSuccessStatusCode();
+        return await response.Content.ReadFromJsonAsync<ReloadResult>(ApiJsonOptions.ClientOptions, ct)
+            ?? throw new InvalidOperationException("Unexpected null from api/reload.");
+    }
+}