🔧 feat: enhance readiness endpoint with detailed connection status

- Upgraded readiness endpoint to provide per-connection health status
- Added structured JSON response with connection details
- Database health status now includes explicit healthy/unhealthy/not_configured states
- Better observability with detailed failure reasons
- Maintains backward compatibility with existing readiness checks

Response Examples:
✅ Healthy: {ready: true, connections: {database: {status: healthy}}}
❌ Unhealthy: {ready: false, reason: database_unhealthy, connections: {database: {status: unhealthy, error: ...}}}
❌ Shutting Down: {ready: false, reason: server_shutting_down, connections: {database: not_checked}}}

Benefits:
- Detailed health information for debugging
- Per-connection status (database, future: cache, etc.)
- Better Kubernetes/container orchestration integration
- Clear failure reasons for troubleshooting
- Extensible for additional services

Testing:
- ✅ Readiness endpoint returns detailed connection status
- ✅ Database health properly reflected
- ✅ All 25 BDD scenarios passing
- ✅ All unit tests passing

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

pkg/server/server.go

@@ -24,6 +24,7 @@ import (
 	userapi "dance-lessons-coach/pkg/user/api"
 	"dance-lessons-coach/pkg/validation"
 	"dance-lessons-coach/pkg/version"
+	"encoding/json"
 
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
@@ -213,12 +214,12 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 // handleReadiness godoc
 //
 //	@Summary		Readiness check
-//	@Description	Check if the service is ready to accept traffic including database connectivity
+//	@Description	Check if the service is ready to accept traffic including detailed connection status
 //	@Tags			System/Health
 //	@Accept			json
 //	@Produce		json
-//	@Success		200	{object}	map[string]bool	"Service is ready"
-//	@Failure		503	{object}	map[string]bool	"Service is not ready"
+//	@Success		200	{object}	object	"Service is ready with connection details"
+//	@Failure		503	{object}	object	"Service is not ready with failure details"
 //	@Router			/ready [get]
 func (s *Server) handleReadiness(w http.ResponseWriter, r *http.Request) {
 	log.Trace().Msg("Readiness check requested")
@@ -227,21 +228,61 @@ func (s *Server) handleReadiness(w http.ResponseWriter, r *http.Request) {
 	select {
 	case <-s.readyCtx.Done():
 		log.Trace().Msg("Readiness check: not ready (shutting down)")
+		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(http.StatusServiceUnavailable)
-		w.Write([]byte(`{"ready":false}`))
+		json.NewEncoder(w).Encode(map[string]interface{}{
+			"ready":  false,
+			"reason": "server_shutting_down",
+			"connections": map[string]interface{}{
+				"database": "not_checked",
+			},
+		})
 		return
 	default:
-		// Server is not shutting down, check database if available
+		// Server is not shutting down, check all connections
+		connectionStatus := make(map[string]interface{})
+		allHealthy := true
+		var failureReason string
+
+		// Check database if available
 		if s.userRepo != nil {
 			if err := s.userRepo.CheckDatabaseHealth(r.Context()); err != nil {
 				log.Warn().Err(err).Msg("Database health check failed")
-				w.WriteHeader(http.StatusServiceUnavailable)
-				w.Write([]byte(`{"ready":false}`))
-				return
+				connectionStatus["database"] = map[string]interface{}{
+					"status": "unhealthy",
+					"error":  err.Error(),
+				}
+				allHealthy = false
+				failureReason = "database_unhealthy"
+			} else {
+				connectionStatus["database"] = map[string]interface{}{
+					"status": "healthy",
+				}
+			}
+		} else {
+			connectionStatus["database"] = map[string]interface{}{
+				"status": "not_configured",
 			}
 		}
-		log.Trace().Msg("Readiness check: ready")
-		w.Write([]byte(`{"ready":true}`))
+
+		if allHealthy {
+			log.Trace().Msg("Readiness check: ready")
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusOK)
+			json.NewEncoder(w).Encode(map[string]interface{}{
+				"ready":       true,
+				"connections": connectionStatus,
+			})
+		} else {
+			log.Warn().Str("reason", failureReason).Msg("Readiness check: not ready")
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusServiceUnavailable)
+			json.NewEncoder(w).Encode(map[string]interface{}{
+				"ready":       false,
+				"reason":      failureReason,
+				"connections": connectionStatus,
+			})
+		}
 	}
 }