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/instances.go

@@ -23,13 +23,15 @@ func (s *Server) listInstances(w http.ResponseWriter, r *http.Request) {
 			respondNotFound(w, "stage")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "failed to get stage: "+err.Error())
+		slog.Error("failed to get stage", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
 	instances, err := s.store.GetInstancesByStageID(stageID)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "failed to list instances: "+err.Error())
+		slog.Error("failed to list instances", "error", err)
+		respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 	respondJSON(w, http.StatusOK, instances)
@@ -51,7 +53,8 @@ func (s *Server) deployInstance(w http.ResponseWriter, r *http.Request) {
 			respondNotFound(w, "project")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "failed to get project: "+err.Error())
+		slog.Error("failed to get project", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
@@ -61,7 +64,8 @@ func (s *Server) deployInstance(w http.ResponseWriter, r *http.Request) {
 			respondNotFound(w, "stage")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "failed to get stage: "+err.Error())
+		slog.Error("failed to get stage", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
@@ -77,7 +81,8 @@ func (s *Server) deployInstance(w http.ResponseWriter, r *http.Request) {
 
 	deployID, err := s.deployer.AsyncTriggerDeploy(r.Context(), projectID, stageID, req.ImageTag)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "failed to trigger deploy: "+err.Error())
+		slog.Error("failed to trigger deploy", "error", err)
+		respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 	respondJSON(w, http.StatusAccepted, map[string]string{
@@ -99,7 +104,8 @@ func (s *Server) removeInstance(w http.ResponseWriter, r *http.Request) {
 			respondNotFound(w, "instance")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "failed to get instance: "+err.Error())
+		slog.Error("failed to get instance", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
@@ -158,7 +164,8 @@ func (s *Server) controlInstance(w http.ResponseWriter, r *http.Request, action
 			respondNotFound(w, "instance")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "failed to get instance: "+err.Error())
+		slog.Error("failed to get instance", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
@@ -187,7 +194,8 @@ func (s *Server) controlInstance(w http.ResponseWriter, r *http.Request, action
 	}
 
 	if controlErr != nil {
-		respondError(w, http.StatusInternalServerError, fmt.Sprintf("failed to %s instance: %v", action, controlErr))
+		slog.Error("failed to control instance", "action", action, "instance_id", instanceID, "error", controlErr)
+		respondError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}