🔧 feat: enhance readiness endpoint with database health check

- Added CheckDatabaseHealth() method to UserRepository interface
- Implemented database connectivity check in SQLite repository
- Enhanced /ready endpoint to verify database health before reporting ready
- Improved readiness logic: checks both server shutdown status and database connectivity
- Better observability: Logs database health check failures with warnings

Benefits:
- More accurate readiness reporting for Kubernetes/container environments
- Detects database connectivity issues before accepting traffic
- Prevents application from accepting requests when database is unavailable
- Maintains backward compatibility with existing readiness checks

Implementation:
- Simple COUNT query to test database responsiveness
- Graceful handling of database unavailability
- Proper HTTP 503 status when not ready
- Comprehensive logging for troubleshooting

Testing:
- ✅ Readiness endpoint returns true when database is healthy
- ✅ Readiness endpoint returns false when database is unhealthy
- ✅ All existing functionality preserved
- ✅ 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

@@ -213,7 +213,7 @@ 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
+//	@Description	Check if the service is ready to accept traffic including database connectivity
 //	@Tags			System/Health
 //	@Accept			json
 //	@Produce		json
@@ -223,12 +223,23 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 func (s *Server) handleReadiness(w http.ResponseWriter, r *http.Request) {
 	log.Trace().Msg("Readiness check requested")
 
+	// Check if server is shutting down
 	select {
 	case <-s.readyCtx.Done():
 		log.Trace().Msg("Readiness check: not ready (shutting down)")
 		w.WriteHeader(http.StatusServiceUnavailable)
 		w.Write([]byte(`{"ready":false}`))
+		return
 	default:
+		// Server is not shutting down, 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
+			}
+		}
 		log.Trace().Msg("Readiness check: ready")
 		w.Write([]byte(`{"ready":true}`))
 	}