Add remove profile picture button to local Puter instance

[brittneylilly]

Description

Added a "Remove" profile picture button to the account settings page.

Motivation

Users currently can upload a profile picture but have no way to remove it and return to the default avatar.

Changes

• Added a remove button in UITabAccount.js — added the button HTML and click handler
• Button appears under the profile picture — placed inside the flex container directly below the profile picture div
• Clicking removes the custom picture and restores the default avatar — the click handler sets the picture to null and updates the UI to show the default

Testing

• Tested uploading a picture then removing it
• Verified default avatar returns correctly

Demo Video

Puter.Demo_remove.profile.picture.mp4