nx_media_run_gate.nx

nx_media_run_gate.nx -- REFEREE for EXPOSURE rung X0 (nx_ppm + nx_media_run). Proves the REAL-FILE path end to end (not synthetic in-memory pixels): 1. build a 64x64 person frame (gray bg + 32x32 skin blob), WRITE it as a real PPM to the staging input path the tool reads. 2. READ it back from disk and PARSE the PPM -> *Image. 3. run presence on the PARSED-FROM-FILE image -> must be PRESENT, skin 250 permille, bbox [16,16..47,47]. 4. PPM write/read ROUND-TRIP: write the parsed image again, re-read, and confirm dims + sample pixels survive (blob pixel = skin, bg pixel = gray). Side effect: leaves knowledge/staging/media/frame.ppm in place so `nx_media_run` can be run immediately afterwards on real input. Every measured value PRINTED. stdout + knowledge/status/media_run_gate.log. Exit 0 GREEN / 1 RED. Sovereign: syscalls + nx_image + nx_ppm + nx_presence. license_tier: ORIGINAL