fix: confusing message display when upload size was greater than the …

[BrainNotFoundException]

…limit.

📌 Purpose

• Fixes the issue where uploading files larger than the 5MB limit showed a confusing 'Failed to upload papers' message instead of the specific error.
• And a missing error display toast for the same.

Corresponding issue: none just found it randomly

🔧 Changes

• Fixed the error message for upload size
• Made error message for invalid files more appropriate