fix: mobile diff comment input placeholder and review comments pill

Use a shorter comment placeholder on mobile (drop the Cmd+Enter hint that has
no touch equivalent) so it no longer clips in the auto-sized textarea.

Add a remove (x) button to the review comments pill, matching the annotation
and dev-server-log pills, and stop the mobile touch-target min-height/width
from inflating the pill close buttons.

packages/ui/src/components/comments/InlineCommentInput.tsx

@@ -147,7 +147,7 @@ export function InlineCommentInput({
           value={text}
           onChange={(e) => setText(e.target.value)}
           onKeyDown={handleKeyDown}
-          placeholder={t('inlineComment.input.placeholder')}
+          placeholder={isMobile ? t('inlineComment.input.placeholderShort') : t('inlineComment.input.placeholder')}
           outerClassName="rounded-[var(--radius-xl)] bg-[var(--surface-subtle)] ring-1 ring-inset ring-border/60 focus-within:ring-2 focus-within:ring-[var(--interactive-focus-ring)]"
           className="min-h-[80px] px-3 py-2.5 text-sm resize-y"
         />