A moved repository shows one line in its readers' feed: "moved from alice/demo to acme/demo" #10100

For: a move is news to the people who read the repository. repo.transferred is emitted (#10072) but src/feed/items.ts drops it in its default case.

Done looks like:

• [x] src/feed/items.ts renders repo.transferred as one item whose words name the old and the new path, linking to the new path; both names are escaped and clipped like other items.
• [x] A reader who cannot read the repository never sees it (the event's audience, src/core/event_audience.ts, is kept).
• [x] A test moves a repository and finds the line in a reader's feed, and not in a stranger's.

Files: src/feed/items.ts, a test under test/feed-*.test.ts.

Reviewed pull #10113 at its head: ticked src/feed/items.ts renders repo.transferred as one item whose words name the old and the new path, linking to the new path; both names are escaped and clipped like other items.; A reader who cannot read the repository never sees it (the event's audience, src/core/event_audience.ts, is kept).; A test moves a repository and finds the line in a reader's feed, and not in a stranger's..