fix(flux2): apply BN normalization to latents for inpainting

[Pfannkuchensack]

Summary

The FLUX.2 Klein transformer operates in BN-normalized latent space, but init_latents from VAE encode were not being normalized before being passed to the InpaintExtension. This caused a scale mismatch when merging intermediate_latents (normalized) with noised_init_latents (unnormalized), resulting in visible artifacts at mask blur boundaries.

Now normalize:

• init_latents_packed before passing to InpaintExtension
• noise_packed for correct interpolation in normalized space
• x (starting latents) for img2img/inpainting workflows

Related Issues / Discussions

Reported issue: Strange artifacts appearing on mask blur regions when using FLUX.2 Klein for inpainting, particularly visible when regenerating over the same region multiple times.

QA Instructions

1. Load a FLUX.2 Klein model
2. Create an inpainting workflow with mask blur enabled
3. Generate multiple times over the same masked region
4. Verify that the artifacts/seams at the mask boundary are no longer visible

Merge Plan

Standard merge, no special considerations needed.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)