web: search across the instance, and a page for the inbox !227

Stacked on !226.

A search command matches repository paths, descriptions and topics, and issue and merge request titles, across everything the caller can read. /search renders it, with a field in the rail on every page. Anonymous visitors get the public rows from the same query — the visibility rule is in the SQL, not a second code path. Issue body search is FTS work and stays with #114.

/notifications lists the inbox from !226, unread by default, and marks rows read. The rail carries the badge; a Watch button sits beside Pin in the repository header.

/explore's filter now calls the same MatchesRepo the command uses instead of its own copy of the rule.

Closes #118 Ref #113