v0.9.7 — Local engine: overlapping chunks (no dropped words)

Fixed

• The local engine split long recordings at hard 25-second boundaries, so a word or its
  punctuation could be lost or duplicated at the seam. Adjacent windows now overlap ~2s and
  the duplicate at the join is trimmed by word match (case/punctuation-insensitive); otherwise
  a plain space-join. Parity with the Windows port, which fixed this first.