Fix Wan JVP image projector checkpoint compatibility - #140

Summary

• restore the Wan image-conditioning projector architecture used by the published I2V checkpoints
• retain affine parameters and the canonical epsilon for both LayerNorm stages in the JVP implementation
• add CPU regression coverage for checkpoint keys, forward equivalence, gradients, and first/last-frame token layout

Why

The JVP implementation constructed the projector with the model's non-affine WanLayerNorm. As a result, pretrained projector normalization weights and biases were dropped during loading, changing the image-conditioning transform. The projector now mirrors the canonical Wan I2V module, so its state dictionary and numerical path are compatible with those checkpoints.

Validation

python -m pytest -q tests/test_wan2pt1_jvp_mlp_proj.py
python -m compileall -q turbodiffusion tests

All three regression tests pass.