The page-by-page and control-by-control description of the swarm UI moves to
4-implementation/web-ui/swarm-ui.md, with the quick-links wiring. The handbook
page keeps the route table, how to reach the UI, who may and what the browser
keeps. Links to the moved sections point at the new page.
The directory covered GitHub and GitLab only; the forge and matrix account
kinds an operator can link were described under the swarm UI page. Two new
pages (forgejo.md, matrix.md) cover linking, what the agent gets and
deleting in operator terms, the directory README lists them, and the UI page
keeps a pointer for each kind.
