feat(server): add recipe constraints and update generation workspace (#2217)

examples/server/recipes/sd-turbo.json

@@ -2,6 +2,7 @@
   "schema_version": 1,
   "id": "sd-turbo",
   "name": "SD Turbo",
+  "size_multiple": 64,
   "description": "Select a single-file SD-Turbo checkpoint. Uses one step with CFG disabled (scale 1 in sd.cpp); use more steps for partial image-to-image denoising.",
   "model_url": "https://huggingface.co/stabilityai/sd-turbo",
   "slots": [