refactor: Enhance file attachment handling and UI components

- Updated the file attachment service to utilize a new LocalAttachment class, improving the management of file metadata such as display names.
- Refactored methods for picking and uploading files to accommodate the new LocalAttachment structure, ensuring consistent handling of file attributes.
- Improved the chat page to validate and manage file attachments more effectively, enhancing user experience during file uploads.
- Added functionality for image previews in the file attachment widget, allowing users to see selected images before sending.
- Introduced a remove button for attachments, improving usability by enabling users to easily discard unwanted files.

lib/shared/services/tasks/task_worker.dart

@@ -107,6 +107,10 @@ class TaskWorker {
             QueuedAttachmentStatus.failed => FileUploadStatus.failed,
             QueuedAttachmentStatus.cancelled => FileUploadStatus.failed,
           };
+          const imageExts = <String>{'.jpg', '.jpeg', '.png', '.gif', '.webp'};
+          final lowerName = task.fileName.toLowerCase();
+          final bool isImage =
+              existing.isImage ?? imageExts.any(lowerName.endsWith);
           final newState = FileUploadState(
             file: File(task.filePath),
             fileName: task.fileName,
@@ -117,6 +121,7 @@ class TaskWorker {
             status: status,
             fileId: entry.fileId ?? existing.fileId,
             error: entry.lastError,
+            isImage: isImage,
           );
           _ref
               .read(attachedFilesProvider.notifier)
@@ -260,6 +265,7 @@ class TaskWorker {
           progress: 0.0,
           status: FileUploadStatus.uploading,
           fileId: existing.fileId,
+          isImage: existing.isImage ?? true,
         );
         _ref
             .read(attachedFilesProvider.notifier)