Add SRT subtitle QC implementation plan
15 tasks: add srt library, build srt_pairing helpers incrementally
(normalise_slug, canonical_locale, parse_*_tokens, score_pair,
pair_batch), thread srt_path through executor, implement the three
SRT checks (structure, timing, language), wire batch pre-flight
pairing, update routes for .srt uploads and pairing-preview endpoint,
add pre-flight UI to configure template (XSS-safe DOM rendering for
user-controlled filenames), register checks in profile, end-to-end
smoke test against testing_15may/srt/.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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