Give every account a profile page and a directory of accounts

Give every account a profile page and a directory of accounts

Clicking a name now opens /u/<name>: the issues and changes somebody
opened, the reviews they gave, the comments they left, and the
repositories that work is in. The numbers and the feed are grouped reads
of the same event rows the activity feed pages through, so a profile
cannot disagree with the feed, and every read is limited to the
repositories the reader may open. A private repository's work is not a
number an outsider gets to learn, so two readers can see different
totals and the page says what its numbers cover.

/u lists the roster. Account names are public on this instance; their
activity is not. Both pages ask crawlers to leave them out of an index.

@name in an issue, a comment, a change request, or a release note links
to the account it addresses, using the mention scanner CI already
evaluates: what reads as an address on the page is what a workflow sees.
A name that is not an account stays text, and code samples are skipped.

Git author names are not linked and commit counts are not shown. A
commit author is a name somebody typed, not the credential that proves
an account, and the index only keeps the top eight authors of each
default branch anyway.