mAi: #2 - phase 1 PoC: ComfyUI on mRock + first FLUX schnell image

Native systemd install (matches Ollama pattern on Arch — Docker on mRock
has no nvidia runtime; native venv via uv is the lighter path). The
Black-Forest-Labs FLUX.1-schnell HF repo is gated, so the download script
points at ungated mirrors (Comfy-Org/flux1-schnell + sirorable/flux-ae-vae)
that ship the same Apache-2.0 weights.

First image — cat in a fishbowl, 1024x1024, 4 steps — generated end-to-end
in 9.79s via curl + workflow JSON; stored at
/home/m/dev/ImaGen/poc/first-image.png on mRiver (not committed; transient
PoC artefact). Go adapter is phase 2.

scripts/flux-schnell-poc.json

@@ -0,0 +1,87 @@
+{
+  "prompt": {
+    "6": {
+      "class_type": "CLIPTextEncode",
+      "inputs": {
+        "text": "a small fishbowl with a cat staring out, photo, soft light",
+        "clip": ["11", 0]
+      }
+    },
+    "8": {
+      "class_type": "VAEDecode",
+      "inputs": {
+        "samples": ["31", 0],
+        "vae": ["10", 0]
+      }
+    },
+    "9": {
+      "class_type": "SaveImage",
+      "inputs": {
+        "filename_prefix": "imagen-poc",
+        "images": ["8", 0]
+      }
+    },
+    "10": {
+      "class_type": "VAELoader",
+      "inputs": {
+        "vae_name": "ae.safetensors"
+      }
+    },
+    "11": {
+      "class_type": "DualCLIPLoader",
+      "inputs": {
+        "clip_name1": "t5xxl_fp8_e4m3fn.safetensors",
+        "clip_name2": "clip_l.safetensors",
+        "type": "flux"
+      }
+    },
+    "12": {
+      "class_type": "UNETLoader",
+      "inputs": {
+        "unet_name": "flux1-schnell.safetensors",
+        "weight_dtype": "fp8_e4m3fn"
+      }
+    },
+    "13": {
+      "class_type": "CLIPTextEncode",
+      "inputs": {
+        "text": "",
+        "clip": ["11", 0]
+      }
+    },
+    "27": {
+      "class_type": "EmptySD3LatentImage",
+      "inputs": {
+        "width": 1024,
+        "height": 1024,
+        "batch_size": 1
+      }
+    },
+    "30": {
+      "class_type": "ModelSamplingFlux",
+      "inputs": {
+        "model": ["12", 0],
+        "max_shift": 1.15,
+        "base_shift": 0.5,
+        "width": 1024,
+        "height": 1024
+      }
+    },
+    "31": {
+      "class_type": "KSampler",
+      "inputs": {
+        "model": ["30", 0],
+        "seed": 1234567,
+        "steps": 4,
+        "cfg": 1.0,
+        "sampler_name": "euler",
+        "scheduler": "simple",
+        "denoise": 1.0,
+        "positive": ["6", 0],
+        "negative": ["13", 0],
+        "latent_image": ["27", 0]
+      }
+    }
+  },
+  "client_id": "imagen-poc-001"
+}