fix: handle Jira ADF description format in issue get/update

Jira API v3 returns descriptions as ADF (Atlassian Document Format)
JSON objects. Changed IssueFields.description from Option<String> to
Option<Value> and added recursive ADF text extraction with support for
paragraphs, headings, ordered/bullet lists, code blocks, mentions,
emoji, inline cards, and status nodes. Also fixed comment body preview.

Author: Your Name