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.Development.json

@@ -4,5 +4,13 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning"
     }
+  },
+  "SurrealDb": {
+    "Namespace": "hubmi",
+    "Database": "hubmi",
+    "DataDirectory": "data",
+    "RemoteUrl": "ws://127.0.0.1:8010/rpc",
+    "Username": "root",
+    "Password": "root"
   }
 }