Initial commit: dnsmasq web UI

- ASP.NET Core 9 Blazor Web App + Web API
- Hosts file management (read/write, hosts(5) format)
- DHCP static hosts (dhcp-host=, dnsmasq config)
- DHCP leases (read-only, dnsmasq lease file format)
- Reload and status commands (configurable)
- Docker: standalone app image + Dockerfile.dnsmasq (app + dnsmasq)
- docker-compose.test.yml: app + dhcp-client, testdata mount
- Unit tests (Hosts, DhcpHost, Leases, DnsmasqConfig parsers) using testdata

src/DnsmasqWebUI/Controllers/DhcpController.cs

@@ -0,0 +1,50 @@
+using DnsmasqWebUI.Models;
+using DnsmasqWebUI.Services.Abstractions;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DnsmasqWebUI.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class DhcpController : ControllerBase
+{
+    private readonly IDnsmasqConfigService _configService;
+    private readonly IReloadService _reloadService;
+
+    public DhcpController(IDnsmasqConfigService configService, IReloadService reloadService)
+    {
+        _configService = configService;
+        _reloadService = reloadService;
+    }
+
+    [HttpGet("hosts")]
+    public async Task<ActionResult<IReadOnlyList<DhcpHostEntry>>> GetHosts(CancellationToken ct)
+    {
+        try
+        {
+            var entries = await _configService.ReadDhcpHostsAsync(ct);
+            return Ok(entries);
+        }
+        catch (Exception ex)
+        {
+            return StatusCode(500, new { error = ex.Message });
+        }
+    }
+
+    [HttpPut("hosts")]
+    public async Task<ActionResult<object>> PutHosts([FromBody] List<DhcpHostEntry>? entries, CancellationToken ct)
+    {
+        if (entries == null)
+            return BadRequest(new { error = "Body required" });
+        try
+        {
+            await _configService.WriteDhcpHostsAsync(entries, ct);
+            var reload = await _reloadService.ReloadAsync(ct);
+            return Ok(new { saved = true, reload = new { reload.Success, reload.ExitCode, reload.StdErr } });
+        }
+        catch (Exception ex)
+        {
+            return StatusCode(500, new { error = ex.Message });
+        }
+    }
+}