fix: accept only jpeg/png in file input

[darshansrc]

Add file type restrictions in native file picker

What's Changed

• Added accept="image/jpeg,image/png" attribute to file input to show supported formats in the native file picker dialog

Why?

• Improves user experience by showing only JPEG and PNG files in the file picker dialog
• Provides clear visual feedback about supported file types before upload attempt
• Reduces confusion about supported file types (prevents users from attempting to upload PDFs or other formats)
• Complements existing backend validation with frontend guidance

Testing

• Verified file picker dialog only shows image files (JPEG, PNG) on both desktop and mobile browsers
• Confirmed backend validation still works as a security measure

[vercel]

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