page-context 0.6 credits and keyword links

Aligned house docs with @antora-supplemental/page-context 0.6:

  • Teaching pages: byline Last updated … by …; authorship and classification in the footer.

  • Agent-assisted source attrs stay {agent} on behalf of {human}; display is {human} (via {agent}).

  • Keywords/Tags link to /home/keywords/{slug}/ (default /home/keywords/{slug}/); hubs register @antora-supplemental/page-context/antora for filtered article trees.

  • page-edit 0.2 adds a lead-table Source row (View | Edit).