Initial commit: JMon cross-platform monitoring system

- gRPC client-server metrics collection
- PeriodicTimer-based 5-second sampling
- Delta encoding with configurable thresholds
- Queue/retry mechanism for resilience
- ProcessId tracking for duplicate detection
- Server-side state reconstruction
- Native AOT compilation support
- Docker/Podman containerization
- PostgreSQL + TimescaleDB persistence layer

JMonAgent/SystemMetrics.cs

@@ -0,0 +1,44 @@
+using System.Text.Json.Serialization;
+
+namespace JMonAgent;
+
+public record SystemMetrics(
+    string MachineName,
+    string OSDescription,
+    double CpuUsagePercentage,
+    long MemoryUsedBytes,
+    long MemoryTotalBytes,
+    long SwapUsedBytes,
+    long SwapTotalBytes,
+    long DiskUsedBytes,
+    long DiskTotalBytes,
+    string DiskMountPoint,
+    DateTime Timestamp,
+    string IpAddress,
+    string HwId,
+    int ProcessId
+);
+
+public record DeltaMetrics(
+    string MachineName,
+    string? OSDescription,
+    double? CpuUsagePercentage,
+    long? MemoryUsedBytes,
+    long? MemoryTotalBytes,
+    long? SwapUsedBytes,
+    long? SwapTotalBytes,
+    long? DiskUsedBytes,
+    long? DiskTotalBytes,
+    string? DiskMountPoint,
+    DateTime Timestamp,
+    string? IpAddress,
+    string? HwId,
+    int ProcessId
+);
+
+[JsonSourceGenerationOptions(WriteIndented = true)]
+[JsonSerializable(typeof(SystemMetrics))]
+[JsonSerializable(typeof(DeltaMetrics))]
+internal partial class MetricsJsonContext : JsonSerializerContext
+{
+}