Slim fixture: mic-detr-slim

A 23.8M-parameter fixture for the detr MIC, covering facebook/detr-resnet-50. It is a test artifact, not a usable model, tagged test-artifact to keep it out of candidate-model search.

• Fixture key 8a01ecc30615. It covers every checkpoint whose processor files are byte-identical and whose config matches after shrinking.
• Same architecture, smaller config: DetrForObjectDetection, shrunk by the generic rule in sweep.py (encoder_layers 2, decoder_layers 2).
• Processor files copied byte for byte from facebook/detr-resnet-50: preprocessor_config.json.
• Random weights (seed 17). They passed the input-sensitivity gate: every perturbation of the contract's inputs moved the logits by at least 0.001 (weakest: pixel_values:swap_channels, 0.0992), so no training was needed.
• Same tensor names as the real checkpoint. The real checkpoint has every parameter, and so does the fixture.
• Saved in float32, the dtype facebook/detr-resnet-50 loads in by default.
• Finite in float32, bfloat16, and float16 (forward, loss, gradients).

Built by build_fixtures.py; build.json records the pinned sources, gate results, and file hashes. The source repository commits only README.md and build.json; rebuild the other files with python example/build_fixtures.py --fixture mic-detr-slim.