QC gate evaluator (hard/soft policy + triage-queue calculator)

A small, dependency-free (pure standard-library) Python tool that makes the article's reference architecture runnable. It models an automated QC policy as a set of checks across the three checkpoints (ingest validation, post-encode quality gate, pre-publish check), each tagged with an EBU-style layer (wrapper/bitstream/baseband/x-check/layout), a severity (hard or soft), a comparator, and a threshold. Given a batch of asset results (JSON or CSV: container_valid, decodes_ok, declared_vs_decoded_m