Fix: Remove unnecessary <br> after image insertion to fix extra line break

[Serranosoft]

This PR removes the redundant line that inserts a <br> after each image (issue related #414) :

exec('insertHTML', "<br/>");

• Every image inserted is wrapped automatically in a <div> block.
• The <div> ensures the cursor is placed correctly so the html will not be empty and the editor remains editable.
• The previous <br> caused unexpected line break after every inserted image.
• This change improves UX by allowing multiple images to be inserted consecutively