issues-fs-lite in issues/, rendered as a kanban and pages in admin

This file is the first proof. Three folders (open, blocked, done), one markdown file per issue with YAML front matter (created, priority, type, parent, owner, source, estimated_effort, tags), moved between folders by mv, committed with the work. The build renders admin/issues (a kanban by status, filter by epic, owner and priority), one page per issue, and counts on the admin page.