add healthcheck route

cmd/api/healthcheck.go

@@ -0,0 +1,21 @@
+package main
+
+import "net/http"
+
+func (app *application) healthcheckHandler(w http.ResponseWriter, r *http.Request) {
+	env := envelope{
+		"status": "available",
+		"system_info": map[string]string{
+			"environment": app.cfg.env,
+			"version":     version,
+		},
+		"foundry": map[string]any{
+			"status":       app.foundryApp.Status,
+			"is_available": app.foundryApp.IsAvailable,
+		},
+	}
+	err := app.writeJSON(w, http.StatusOK, env, nil)
+	if err != nil {
+		app.serverErrorResponse(w, r, err)
+	}
+}