mohdel v0.112.0

Added

• POST /v1/transcription on thin-gate's data plane — closes the
  "factory path only" gap from 0.111.0; the cross-process client can
  now transcribe via callTranscription(envelope, { socketPath })
  from mohdel/client. Same one-shot shape as /v1/image: plain JSON
  response, no streaming, no enforcer, op: "transcription" driver
  tag. audio.fileUri is file:// (gate sessions read the path —
  requires a shared filesystem with the caller) or data: (inline,
  subject to the 16 MiB body cap). Rust protocol structs
  (TranscriptionEnvelope / TranscriptionResult), conformance
  fixtures, and an end-to-end session-dispatch test included; the
  image and transcription paths now share one one-shot pool-exchange
  helper in the gate.