Add support for agent-friendly content generation

[chalin]

Tasks

• Create plan for feature, defining goals, scope, etc. - Add agent-friendly support plan and phase 1 implementation of Markdown output #2597
• Support Markdown output format
  • Add agent-friendly support plan and phase 1 implementation of Markdown output #2597
  • Cleanup: Drop Markdown output fmt since Hugo defines it #2599
  • Trim spaces from titles and descriptions in layouts/all.md #2600
  • Add View Markdown page-meta link #2601
  • Add a first-cut for post_view_markdown to all i18n files #2602
• Support llms.txt
  • Base implementation - Add LLMS output and llms.txt support, enables it over docsy.dev #2605
  • Housekeeping (bump our afdocs score): Project docs: allow default outputs, including md #2606
  • ...

Notes

Other considerations:

• Generate full URLs in the markdown? This doesn't seem to be required from the research I've done, but might be helpful? Is it worth it?
• Add i18n tag for "Section pages". Other keywords? "Page information", "Description"?