refactored HTTP error handling and streamlined UI components by centralizing shared logic and removing redundant parameters

lib/utils/downloads/download_manager.dart

@@ -36,7 +36,6 @@ class DownloadManager {
 
   final Map<String, DownloadJob> _jobs = {}; // keyed by remotePath
   final Map<String, DownloadJob> _byTaskId = {};
-  final Map<String, bd.DownloadTask> _taskById = {};
 
   /// All jobs the user should currently see in the downloads tray/overview:
   /// everything that is in progress or finished-but-not-yet-opened (failed
@@ -134,7 +133,6 @@ class DownloadManager {
     )..taskId = task.taskId;
     _jobs[remotePath] = job;
     _byTaskId[task.taskId] = job;
-    _taskById[task.taskId] = task;
     _refreshVisible();
 
     final ok = await bd.FileDownloader().enqueue(task);
@@ -217,10 +215,7 @@ class DownloadManager {
         job.status.value = const DownloadCancelled();
       }
       _jobs.remove(job.remotePath);
-      if (taskId != null) {
-        _byTaskId.remove(taskId);
-        _taskById.remove(taskId);
-      }
+      if (taskId != null) _byTaskId.remove(taskId);
       scheduleMicrotask(job.dispose);
     }
     _refreshVisible();
@@ -314,10 +309,7 @@ class DownloadManager {
   void _remove(DownloadJob job) {
     _jobs.remove(job.remotePath);
     final taskId = job.taskId;
-    if (taskId != null) {
-      _byTaskId.remove(taskId);
-      _taskById.remove(taskId);
-    }
+    if (taskId != null) _byTaskId.remove(taskId);
     _refreshVisible();
     scheduleMicrotask(job.dispose);
   }