Slim fixture: mic-vit-slim

A 0.2M-parameter fixture for the vit MIC, covering google/vit-base-patch16-224. It is a test artifact, not a usable model, tagged test-artifact to keep it out of candidate-model search.

• Fixture key 3fc8366aafe8. It covers every checkpoint whose processor files are byte-identical and whose config matches after shrinking.
• Same architecture, smaller config: ViTForImageClassification, shrunk by the generic rule in sweep.py (num_hidden_layers 2).
• Processor files copied byte for byte from google/vit-base-patch16-224: preprocessor_config.json.
• Overfit to the contract's training step (300 steps). Random weights failed the input-sensitivity gate: pixel_values:reverse moved the logits by only 5.9e-05 (threshold 0.001).
• Same tensor names as the real checkpoint. The real checkpoint has every parameter, and so does the fixture.
• Saved in float32, the dtype google/vit-base-patch16-224 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-vit-slim.