feat: expanded health checks, deploy filtering, per-project notifications, error sanitization, and audit trail

- Expand health endpoint to check DB, Docker, and NPM connectivity (FUNC-M4)
- Add project_id, stage_id, offset query params to deploys endpoint (FUNC-M5, FUNC-M6)
- Add notification_url field to Stage model for per-project overrides (FUNC-M2)
- Add NPM Ping method for health checking
- Sanitize all internal error messages in API handlers (SEC-M4)
- Add audit trail events for admin actions (FUNC-M3)
- Add EventLog event type to event bus

internal/api/config_export.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"log/slog"
 	"net/http"
 
 	"github.com/alexei/docker-watcher/internal/config"
@@ -10,7 +11,8 @@ import (
 func (s *Server) exportConfig(w http.ResponseWriter, r *http.Request) {
 	data, err := config.ExportConfig(s.store)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "failed to export config: "+err.Error())
+		slog.Error("failed to export config", "error", err)
+		respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}