web: tell a database outage from a missing database

loadRepoForBrowse turned any error from GetRepoByOwnerAndName into a 404, so a
metadata store that could not answer told every reader on the instance that
their database does not exist — for as long as Postgres was down, in the voice
reserved for "there is nothing here". loadRepoForAdmin did the same on the
settings page.

Both classify through repoLookupFailed now: db.ErrNotFound keeps the 404, and
it stays the same 404 the visibility rule renders for a PRIVATE database the
caller may not see, so a masked database and a missing one remain
indistinguishable. Anything else is a 500 through the shared error page, with
the cause logged (slog + scribe.Err) and never rendered.

beads: report a clipped read from every projection

mcpsrv: name the cursor a commit-log miss was asked about

browse: say which cells are actually NULL

mcpsrv: a bad commit-log cursor is a miss, not a fault

web: link issue ids to the tracker that owns them

mcpsrv: answer what is ready across every tracker

browse: report an unparseable start hash as a missing ref

remoteapi: gofmt the integration test

doltsrht: serve /mcp on the web listener

mcpsrv: list the memories a tracker holds

web: drop the author from a memory's revision line

web: answer what is ready across every tracker

mcpsrv: add the beads tools

web: register the views in one explicit list

web: give bd memories their own view

mcpsrv: add the generic browse tools

web: offer the bd command for the issue on screen

db: list every database a viewer may see

web: show how fresh a beads view is

handleView now reads the head commit of the rendered ref onto the envelope
(Head *browse.CommitInfo), and the beads and milestones headers carry a
shared beadsHead partial: <branch> · last commit <relative> · <short hash>,
the hash linking to the commit page and the exact stamp in the title.

The read is decoration on top of an answer: a database with no commits, or
a Log that fails, renders the page without the line rather than 500ing.

The relative time is a new ago func rather than chrome's reltime — it is
past-facing (clock skew reads as "just now", never "in 3 minutes") and
reads a package clock a test can pin.