feat(backend): integrate SurrealDB storage with embedded RocksDB

Add StorageService backed by SurrealDB using the embedded RocksDB provider that persists to ./data (never in memory). Support an optional remote server via SurrealDb:RemoteUrl for frontend sync. Expose readiness and storage probe endpoints under /api/system and add a helper script to start a local SurrealDB server.

Set the backend version to 0.0.1.

backend/Services/IStorageService.cs

@@ -0,0 +1,14 @@
+using TarninaHub.Models;
+
+namespace TarninaHub.Services;
+
+public interface IStorageService
+{
+    Task InitializeAsync(CancellationToken cancellationToken);
+
+    StorageInfo GetInfo();
+
+    Task<int> GetProbeCountAsync(CancellationToken cancellationToken);
+
+    Task<StorageProbe> AddProbeAsync(CancellationToken cancellationToken);
+}