Slim fixture: mic-wav2vec2-slim

A 4.3M-parameter fixture for the wav2vec2 MIC, covering facebook/wav2vec2-base-960h. It is a test artifact, not a usable model, tagged test-artifact to keep it out of candidate-model search.

• Fixture key 447dc0f39f22. It covers every checkpoint whose processor files are byte-identical and whose config matches after shrinking.
• Same architecture, smaller config: Wav2Vec2ForCTC, shrunk by the generic rule in sweep.py (num_hidden_layers 2).
• Processor files copied byte for byte from facebook/wav2vec2-base-960h: feature_extractor_config.json, preprocessor_config.json, special_tokens_map.json, tokenizer_config.json, vocab.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: input_values:roll_batch, 0.603), so no training was needed.
• Same tensor names as the real checkpoint. The real checkpoint lacks wav2vec2.masked_spec_embed, so the fixture omits it too, and loading initializes it as it does for users.
• Saved in float32, the dtype facebook/wav2vec2-base-960h 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-wav2vec2-slim.