Default workflows to SDXL CyberRealistic; ship empty model preseed

Drops the SD 1.5 placeholder. The shipped txt2img/img2img workflows now
reference CyberRealisticXLPlay_V8.0_FP16.safetensors (the checkpoint
figment used in production), and comfyui-init-models.sh ships with no
active fetches — operators uncomment examples or add their own URLs.

The script + workflow filenames have to line up; README explains.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workflows/img2img.json

@@ -17,7 +17,7 @@
   "4": {
     "class_type": "CheckpointLoaderSimple",
     "inputs": {
-      "ckpt_name": "v1-5-pruned-emaonly.safetensors"
+      "ckpt_name": "CyberRealisticXLPlay_V8.0_FP16.safetensors"
     }
   },
   "6": {

workflows/txt2img.json

@@ -17,7 +17,7 @@
   "4": {
     "class_type": "CheckpointLoaderSimple",
     "inputs": {
-      "ckpt_name": "v1-5-pruned-emaonly.safetensors"
+      "ckpt_name": "CyberRealisticXLPlay_V8.0_FP16.safetensors"
     }
   },
   "5": {