Closes the last parity gap. wiki list returns {path, home, pages};
wiki show returns the page source plus its file name, which is what
picks the renderer — the pages here are .org as often as .md.
Listing puts the landing page first and marks it. Editing stays a push, same as every other surface.
Tests: 8 unit, plus testWikiFlows in the live smoke suite (passed
against gitbay.org — org markup renders as prose, not raw #+title:).