log: bridge dolt's remotesrv logger into slog

remotesrv takes a *logrus.Entry and nothing else, so passing nil left it
writing through logrus' standard logger: its own format, its own stream,
and no mask between a field named token and the journal. It is the half
of this process that serves clones and pushes — the likeliest place for
a credential to reach a log field, and the one that was logging around
everything the previous commit configured.

internal/logrusbridge hands it an entry whose only exit is a
logrus.Hook: output to io.Discard, a formatter that produces nothing,
and the logrus level left wide open so the slog handler does the
filtering from the one setting in config.ini. Fields cross as attributes
rather than a formatted blob, which is what lets a mask keyed on the
attribute path fire at all.

Verified against logrus v1.9.3 rather than assumed: Entry.log fires
hooks before it writes, before Logger.Exit and before the panic, so a
Fatal or Panic record reaches slog before the process ends. Both arms
are tested.

The package takes nothing from this service and belongs beside scribe in
auxilia; it is here because it was needed here first.

log: replace logrus with slog behind auxilia's scribe handler

Every logger field this service owned was a *logrus.Entry threaded
through a constructor, which is what logrus costs for want of a usable
default. They are slog.Default().With("component", ...) now, and the
threading is gone with them; the shared middleware's panic reports land
in the same handler, which is why the daemon sets the default before
anything that can fail.

The handler is scribe's tint handler: level from [dolt.sr.ht]log-level,
source positions, and masks keyed on the attribute path for the three
credentials this service handles — the unified-login cookie, the
Internal fernet token and the Authorization header the remotesapi reads
a PAT or a keypair JWT out of. Errors go through scribe.Err, so a culpa
error's hint reaches the operator on its own line.

logrus stays in go.mod: dolt's remotesrv.ServerArgs takes a
*logrus.Entry and nothing else. It is now confined to Config.DoltLogger,
which is the only place this service names it.

dolt-git-hook is deliberately untouched: what it writes to stderr is the
notice a pushing user reads through git, not a log.

feat(remoteapi): auto-create databases on first push to own namespace

Push-to-create: an authenticated, non-suspended caller pushing (or
cloning) an unknown repo under their OWN namespace has it transparently
created — a PRIVATE repository row plus a genuinely empty on-disk NBS
store — then proceeds through the normal ACL check as the owner. Any
other case (anonymous, suspended, another user's namespace, invalid
name) still returns NotFound, so a stranger's namespace is never leaked
and nothing is created.

storage.InitEmptyStore creates the store WITHOUT WriteEmptyRepo: an
"Initialize data repository" commit would make the client's first push a
non-fast-forward and be rejected. An empty store (root = empty hash) lets
the initial push land as the repo's first history. The interceptor
auto-create is race-safe (ErrNameTaken re-fetch) and rolls the row back
if the store cannot be created.

Proven end-to-end (integration): a real `dolt push` to a new name
auto-creates PRIVATE + fast-forwards + re-clones; a foreign-namespace
push is denied with no row created. All prior clone/push/ACL scenarios
still pass.

rename module to sourcecraft.dev/bigbes/sr-ht-dolt; depend on sourcecraft sr-ht-core

remoteapi: authz interceptors, remotesrv assembly, credentials service