CLI and output polish from 1.6.0 release QA #922

Smaller CLI and output issues found in 1.6.0 release QA:

• Predict --json has two shapes under schema_version: 1 (streaming vs not), and class changes type between them.
• quiet=true does not silence stderr (val with json=true, the video progress bar).
• half is forwarded to exported runtimes where it is a no-op; the code comment says FP16.
• export nms=true on YOLO9-E2E exits format_precision_unsupported, a misleading code.
• CLI pose val prints an all-zero summary; CLI semantic predict prints "(no detections)".
• eval_backend shows "pycocotools ?".
• libreyolo models --json omits SenseNova-Vision and LibreMODUS.
• CLI run names are exp where Python uses <family>_exp (e.g. dfine_exp).
• A fresh run logs "Resumed past no-aug threshold (epoch 0 > -14)".
• coco8-pose leaves ~811 MB of COCO annotations behind.
• The GTR semantic LoRA error message names the wrong task.
• README "One API, twenty tasks": act (LibreVLA) and detect3d need more than a different checkpoint; say so next to the example.