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

examples/server/recipes/pid.json

@@ -2,6 +2,7 @@
   "schema_version": 1,
   "id": "pid",
   "name": "PiD (Flux / Z-Image VAE)",
+  "size_multiple": 1,
   "description": "Supply a reference image; the first image is used as the source latent. Select a Flux/Z-Image PiD checkpoint and matching Flux VAE.",
   "model_url": "https://huggingface.co/nvidia/PiD",
   "slots": [