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>

src/GmRelay.Bot/Program.cs

@@ -6,6 +6,7 @@ using GmRelay.Bot.Features.Reminders.SendOneHourReminder;
 using GmRelay.Bot.Features.Sessions.CreateSession;
 using GmRelay.Bot.Features.Sessions.RescheduleSession;
 using GmRelay.Bot.Infrastructure.Database;
+using GmRelay.Bot.Infrastructure.Health;
 using GmRelay.Bot.Infrastructure.Logging;
 using GmRelay.Bot.Infrastructure.Scheduling;
 using GmRelay.Bot.Infrastructure.Telegram;
@@ -85,6 +86,9 @@ builder.Services.AddSingleton<ISessionTriggerStore, DbSessionTriggerStore>();
 builder.Services.AddHostedService<SessionSchedulerService>();
 builder.Services.AddHostedService<RescheduleVotingDeadlineService>();
 
+// ── Health check server ──────────────────────────────────────────────
+builder.Services.AddHostedService<BotHealthCheckHostedService>();
+
 var host = builder.Build();
 
 // ── Run database migrations on startup ───────────────────────────────