Engram 0.15.14

Fixed

• Reuse merged cross-galaxy edges during verified node appends when edge
  visibility cannot change. Track missing endpoints so newly arriving nodes
  still reveal the appropriate edges.
• Preserve first-wins edge precedence and ordering, and rebuild after edge,
  filter, node edit, removal, or galaxy changes. Add six integration regressions
  covering incremental reuse and fallback behavior.

This avoids repeated full edge merges during eligible appends. Live measurements
are still required to establish startup or frame-rate improvement.