v1.9.31 — CLI `opencut polish`

New opencut polish <file> subcommand runs the full v1.9.29 Interview Polish pipeline against a locally running backend. Auto-detects the port (or use --port), submits the job, polls to completion, prints a Rich step table + output paths. Non-zero exit on any failure so it composes with shell scripts and task schedulers.

Flags: --no-repeats, --no-fillers, --no-chapters, --timeout, -o/--output.

No backend changes. See commit 83293b8.