fix: /files total count from DB (was hardcoded 0)

src/api/identity_api.rs

@@ -98,9 +98,11 @@ async fn list_files(
         })
         .collect();
 
+    let total = state.db.count_files().await.map_err(|e| (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
+
     Ok(Json(FilesResponse {
         success: true,
-        total: 0, // TODO: Implement count query
+        total,
         page,
         page_size,
         data,