refactor(doc): one route from a revision to an Archive (spec-wcr #2, #4)

doc.Scan/DocumentSource were production-dead after service.Archive landed —
their only consumer was doc's own test fixture — and they were the seam that
made web's layering violation writable: a surface could reach past service/
into gitx and build its own archive. Deleted, so doc/ now owns no way to read
a revision and service.Archive is the single route from rev to Archive. The
fixture reads through ListDocuments + FromDocuments instead.

TestScanReportsGitErrors covered an unknown revision failing rather than
walking empty, which gitx did not test itself. Relocated there as
TestWalkOfAnUnknownRevisionFails rather than dropped.

linkHierarchy passed path.Dir(p.Path) where every other call site passes DirOf.
Unobservable today: the two differ only at the space root, and there the
section-proximity step is subsumed by the same-directory step above it, so "."
only ever skipped a lookup that had already answered. Verified by reverting and
re-running. Changed anyway — it stays unobservable only by coincidence of two
ranking rules — with a test pinning the invariant that `parent:` resolves to
whatever the same wikilink in the body resolves to.

spec-wcr

chore(beads): enable Dolt auto-push to dolt.srht.bigb.es

Beads changes were only reaching the remote on a manual bd dolt push, so
issue state drifted from the tracker between sessions. bd has native
auto-push (debounced, pushes to the configured origin remote); it was
simply never enabled — sync.remote was set but dolt.auto-push was unset.

Enable it with an explicit 5m debounce rather than relying on the implicit
default. Verified end-to-end: a write fires "dolt auto-push: pushed
successfully", and a fresh dolt clone of the remote shows this session's
closed beads (spec-jjo, spec-mfm, spec-ejq.1) as closed.

Also commits the JSONL exports, which were stale from this session's work.

chore(beads): track the spec.sr.ht issue backlog

Seven issues under the epic: Phases 3-5 (write plane -> review UI ->
deferred pile, chained by blocks), the loose-ends bucket of latent bugs,
and two ops tasks (nav restart, stale apk pins). Exported to a
git-tracked JSONL so the backlog is durable and portable, not only in the
local embedded Dolt DB.