Fix LinkedIn posts being silently truncated mid-text (e.g. at the first parenthesis).
LinkedIn's /rest/posts commentary uses the "little" text format, where \ | { } @ [ ] ( ) < > # * _ ~ are reserved and must be backslash-escaped — unescaped, LinkedIn cuts the post body at the first one (so a post could publish "successfully" yet only show its first sentence, with no "…more"). Commentary is now escaped before sending: URLs are left intact so they still auto-link, and #hashtags stay clickable.