docs: read_rows answers strings or null

beads: stop flattening a stored NULL string

mcpsrv: answer a real NULL as null

web: stop printing store paths to the owner

web: stop printing browse errors to the reader

The overview rendered the browse layer's own error text into the page, under
"Could not read history: " — dolt internals and the store's path on our disk,
which nothing else on this surface discloses and which a reader can do nothing
with.

The page now carries a fixed sentence and the reason goes to the log with the
database id (slog + scribe.Err). The view field is a bool rather than a message,
so no error string can reach the template by being assigned to it later. The
empty-database state the page already reported ("No commits.") is untouched:
that is a fact about the database, not a failure.

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