proxy.js: the empty-source guard tripped on growing VC-3/DNxHD MXF masters,
which carry a valid decodable video stream but report format.duration=N/A
(durationMs=null). Only bail when there is ALSO no resolution (the true
aborted-capture signature), so MXF masters transcode instead of erroring.
Verified: burn-test growing masters now migrate SMB->S3 AND generate proxies
(assets dc0/dc2/dc6 ready with proxy, tags s3).
conform.js: pin codec-correct pixel format per preset (ProRes HQ yuv422p10le,
ProRes 4444 yuva444p10le, DNxHR HQ yuv422p); only emit -preset/-crf for
libx264/libx265 (dnxhd/prores drive quality via profile); and use the
codec-correct output extension in the error handler (was hard-coded .mp4, so a
failed ProRes/DNxHR conform never flipped to error and spun in processing
forever - the broadcast-vs-web asymmetry). All presets verified rc=0.
e64281c9fd