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/appsettings.json

@@ -5,5 +5,10 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+  "SurrealDb": {
+    "Namespace": "hubmi",
+    "Database": "hubmi",
+    "DataDirectory": "data"
+  }
 }