feat(api): add system resource monitoring functionality

- implement getSystemInfo to gather CPU and memory usage
- add platform-specific implementations for memory and CPU usage
- enhance OpenAPI documentation to include system resource metrics

internal/api/system_other.go

@@ -0,0 +1,11 @@
+//go:build !linux && !darwin && !windows
+
+package api
+
+func getMemoryInfo() (total, used uint64) {
+	return 0, 0
+}
+
+func getCPUUsage() float64 {
+	return 0
+}