fix(mcp-image-gen): fix Heretic/FLUX2 integration bugs

- Fix syntax error in server.py (dangling docstring lines)
- Correct model filename: flux-2-klein-4b.safetensors (without -fp8)
- Fix _WORKFLOW_REGISTRY key to match actual downloaded filename
- Update get_models() to always include registry models as fallback
- Fix test expectations to match corrected model names
- All 37 tests passing

mcp/mcp-image-gen/src/workflows/flux2_klein_heretic.json

@@ -0,0 +1,73 @@
+{
+  "6": {
+    "class_type": "CLIPTextEncode",
+    "inputs": {
+      "clip": ["30", 0],
+      "text": "PROMPT_PLACEHOLDER"
+    }
+  },
+  "8": {
+    "class_type": "VAEDecode",
+    "inputs": {
+      "samples": ["13", 0],
+      "vae": ["31", 0]
+    }
+  },
+  "9": {
+    "class_type": "SaveImage",
+    "inputs": {
+      "filename_prefix": "mcp-image-gen",
+      "images": ["8", 0]
+    }
+  },
+  "13": {
+    "class_type": "KSampler",
+    "inputs": {
+      "cfg": 1.0,
+      "denoise": 1.0,
+      "latent_image": ["27", 0],
+      "model": ["32", 0],
+      "negative": ["33", 0],
+      "positive": ["6", 0],
+      "sampler_name": "euler",
+      "scheduler": "beta",
+      "seed": 42,
+      "steps": 4
+    }
+  },
+  "27": {
+    "class_type": "EmptySD3LatentImage",
+    "inputs": {
+      "batch_size": 1,
+      "height": 1024,
+      "width": 1024
+    }
+  },
+  "30": {
+    "class_type": "CLIPLoader",
+    "inputs": {
+      "clip_name": "qwen_3_4b_heretic.safetensors",
+      "type": "flux"
+    }
+  },
+  "31": {
+    "class_type": "VAELoader",
+    "inputs": {
+      "vae_name": "flux2-vae.safetensors"
+    }
+  },
+  "32": {
+    "class_type": "UNETLoader",
+    "inputs": {
+      "unet_name": "flux-2-klein-4b.safetensors",
+      "weight_dtype": "fp8_e4m3fn"
+    }
+  },
+  "33": {
+    "class_type": "CLIPTextEncode",
+    "inputs": {
+      "clip": ["30", 0],
+      "text": "NEGATIVE_PLACEHOLDER"
+    }
+  }
+}