[FEATURE] Accept a link format in hook `systemMessage`: OSC 8 or markdown, as statusline and assistant output do

Problem Statement

systemMessage is a hook's only surface, and accepts no link format.
2.1.246, iTerm2, FORCE_HYPERLINK=1. Accept in systemMessage OSC 8 for urls or accept other format like markdown [title](url) and reformat it to OSC 8 (if you don't like escape chars) - this will allow printing clickable urls to PRs in hooks.

Priority

Medium

Feature Category

Interactive mode (TUI)

Use Case Example

oldest — [Expose proper tests logs](https://github.com/…/issues/92886)
highest — [Remove unused amd-xlarge pools](https://github.com/…/pull/69819)

Wanted: underlined titles; today, unclickable ones or a URL row each.

Additional Context

#70161, #21586, #23438 (statusline OSC 8); #83508; #89084; #88563; #64643.