v1.34.58

Fixed — Singleton-layer smoothing (mermaid-text 0.45.0)

When ascii-dag inserts long-edge dummy nodes during coordinate
assignment, a layer can end up containing a single visible node
that still carries the perpendicular offset induced by hidden
dummies after the dummies are dropped. Visible in the README's
Worker node floating above the RabbitMQ → Worker → PostgreSQL
corridor. New post-pass in sugiyama_layout recenters singleton
visual layers against the median of their real neighbours.

Conservative by design: singleton-only (no ordering changes),
transit-only (sources/sinks excluded after observing they add
crossings), and operates on an immutable position snapshot for
deterministic output. Pinned by
singleton_dependency_layer_tracks_neighbor_median.

26 snapshots updated, all Bucket A (improvement) or Bucket B
(neutral reorganisation). 19/19 crossings tests still pass.