feat: add health check endpoints for Bot and Web

- Web: add /health endpoint with PostgreSQL readiness check (returns 200+JSON or 503)
- Web: add /alive endpoint for liveness probe
- Bot: add BotHealthCheckHostedService serving /health on port 8081 via HttpListener
- Bot: expose port 8081 in Dockerfile and install wget for healthcheck
- compose.yaml: add healthcheck sections for bot and web services
- tests: add TDD tests for both health endpoints

Bump version -> 1.16.0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/GmRelay.Bot.Tests/Infrastructure/Health/BotHealthCheckHostedServiceTests.cs

@@ -0,0 +1,42 @@
+using System.Net;
+using GmRelay.Bot.Infrastructure.Health;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace GmRelay.Bot.Tests.Infrastructure.Health;
+
+public sealed class BotHealthCheckHostedServiceTests : IDisposable
+{
+    private readonly BotHealthCheckHostedService _service;
+
+    public BotHealthCheckHostedServiceTests()
+    {
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["HealthCheck:Prefix"] = "http://localhost:8081/"
+            })
+            .Build();
+
+        _service = new BotHealthCheckHostedService(
+            NullLogger<BotHealthCheckHostedService>.Instance,
+            config);
+    }
+
+    public void Dispose()
+    {
+        _service.StopAsync(CancellationToken.None).Wait(TimeSpan.FromSeconds(5));
+    }
+
+    [Fact]
+    public async Task HealthEndpoint_ShouldReturn200_WhenServiceIsRunning()
+    {
+        await _service.StartAsync(CancellationToken.None);
+
+        using var client = new HttpClient();
+        client.Timeout = TimeSpan.FromSeconds(5);
+        var response = await client.GetAsync("http://localhost:8081/health");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+}