Add FLUX.1 Krea dev to the image model catalog

Krea's guidance-distilled FLUX.1-dev finetune keeps the exact dev layout, so it
runs under the existing flux.1 family unchanged. Wire it up end to end:

- Catalog group with the gated official bf16 pipeline and the open QuantStack
  GGUF quants; the gated artifact is skipped on auto-routing when undownloaded.
- Trust the official repo for non-GGUF from_pretrained loads, next to the other
  black-forest-labs bases.
- Generation defaults: 28 steps at guidance 4.5 per the model card. The generic
  "krea" defaults key (Krea-2-Turbo's 8-step no-CFG recipe) used to swallow the
  id, which would have produced garbage output; the new flux.1-krea key precedes
  it on both the backend table and the images page table.
- The flux.1 prequant checkpoints are schnell-based; the loader's baked
  base_model_id validation refuses them for the Krea-dev base, so int8/fp8
  requests dense-quantize instead (covered by existing prequant tests).

studio/backend/core/inference/diffusion.py

@@ -284,6 +284,9 @@ _TRUSTED_NON_GGUF_REPOS = frozenset(
         "black-forest-labs/flux.1-dev",
         "black-forest-labs/flux.1-schnell",
         "black-forest-labs/flux.1-kontext-dev",
+        # Krea's guidance-distilled FLUX.1-dev finetune: same arch/layout as dev (FluxPipeline,
+        # CLIP+T5+ae), gated like dev. Detected as the flux.1 family via the "flux.1" token.
+        "black-forest-labs/flux.1-krea-dev",
         "tongyi-mai/z-image-turbo",
         "qwen/qwen-image",
         "qwen/qwen-image-2512",