v4.5.1

Added

• styleproof-ci --spec-ref <ref>: on a cold base capture, when the base commit
  already contains the configured --spec path, overlay that file's bytes from
  <ref>:<spec> for the base render only (app source and lockfile stay at --base).
  The overlay is hidden from the dirty-tree gate with a narrowly scoped
  assume-unchanged index flag and is always cleared before the head checkout,
  including after a failed base capture. Omitted --spec-ref preserves 4.5.0 behavior.
  Invalid refs, missing specs at the ref, or absolute/out-of-repo spec paths fail loudly.