Fix upload button rendering on top of text in comment input

[Copilot]

The cloud-upload button in the comment input was absolutely positioned over the textarea, causing it to overlap user-entered text. The previous padding-bottom: 28px workaround only reserved space at the very end of the textarea content, so any wrapped or scrolled lines still rendered behind the button.

Changes

• webviews/editorWebview/index.css, webviews/activityBarView/index.css: drop position: absolute on .textarea-wrapper .comment-upload-button and let it flow as a flex row beneath the textarea (the wrapper is already flex-direction: column). Remove the now-unnecessary padding-bottom: 28px on the textarea.

.textarea-wrapper .comment-upload-button {
    align-self: flex-start;
    margin: 2px 0 4px 4px;
    /* …unchanged styling… */
}

The button now sits below the input anchored to the bottom-left, so it can no longer overlap text. The top-right .title-action (sparkle/generate) remains absolutely positioned and is unaffected.