feat: downloader for Qwen-Image weights, switch-model.sh script

Two frontier tickets from the ComfyUI map (#38), both unblocked now
that their blockers (#39 model choice, #40 lazytainer research) are
resolved.

- downloader-comfyui service (docker-compose.yml) + COMFYUI_* vars
  (.env.example): fetches Qwen-Image FP8 diffusion/text-encoder/VAE
  weights from Comfy-Org/Qwen-Image_ComfyUI, same test -f guard
  pattern as the existing downloaders. Closes #42.
- scripts/switch-model.sh: swaps GPU residency between llama-server
  and comfyui via direct `docker compose stop`/`up -d`, bypassing
  lazytainer per docs/research/lazytainer-omniroute-idle-stop.md
  (its packet-threshold detector can't distinguish OmniRoute's health
  checks from real traffic, so idle-stop can't be relied on for a
  deliberate swap). llama-server-fast stays resident throughout —
  not part of this swap. Closes #43.
- scripts/update.sh: runs the new downloader profile.

docker compose config -q validated clean.

Refs #38, #42, #43

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MrnMEdzeQzqZE5soVEXPCx

docker-compose.yml

@@ -116,6 +116,39 @@ services:
         curl -L --fail --create-dirs -o /models/${LLAMA_FAST_MODEL_FILE:-Qwen3-4B-Instruct-2507-UD-Q8_K_XL.gguf}
         https://huggingface.co/unsloth/Qwen3-4B-Instruct-2507-GGUF/resolve/main/${LLAMA_FAST_MODEL_FILE:-Qwen3-4B-Instruct-2507-UD-Q8_K_XL.gguf}
 
+  # Fetches the three Qwen-Image FP8 files ComfyUI needs (diffusion model,
+  # text encoder, VAE) — same test -f guard pattern as downloader/
+  # downloader-fast above. See docs/research/image-generation-model-choice.md
+  # and issue #42.
+  #
+  # ponytail: target paths assume ComfyUI's standard models/ layout under
+  # BASE_STORAGE_PATH (/storage) — same "not independently confirmed against
+  # the image's Dockerfile" caveat already flagged on the comfyui service
+  # below. If ComfyUI doesn't pick these up, check its actual models root
+  # first.
+  downloader-comfyui:
+    image: curlimages/curl:latest
+    profiles: ["tools"]
+    user: root
+    volumes:
+      - comfyui-data:/storage
+    entrypoint: ["sh", "-c"]
+    command:
+      - >
+        mkdir -p /storage/models/diffusion_models /storage/models/text_encoders /storage/models/vae &&
+        (test -f /storage/models/diffusion_models/${COMFYUI_DIFFUSION_MODEL_FILE:-qwen_image_fp8_e4m3fn.safetensors} &&
+        echo "diffusion model already downloaded, skipping" ||
+        curl -L --fail --create-dirs -o /storage/models/diffusion_models/${COMFYUI_DIFFUSION_MODEL_FILE:-qwen_image_fp8_e4m3fn.safetensors}
+        https://huggingface.co/Comfy-Org/Qwen-Image_ComfyUI/resolve/main/split_files/diffusion_models/${COMFYUI_DIFFUSION_MODEL_FILE:-qwen_image_fp8_e4m3fn.safetensors}) &&
+        (test -f /storage/models/text_encoders/${COMFYUI_TEXT_ENCODER_FILE:-qwen_2.5_vl_7b_fp8_scaled.safetensors} &&
+        echo "text encoder already downloaded, skipping" ||
+        curl -L --fail --create-dirs -o /storage/models/text_encoders/${COMFYUI_TEXT_ENCODER_FILE:-qwen_2.5_vl_7b_fp8_scaled.safetensors}
+        https://huggingface.co/Comfy-Org/Qwen-Image_ComfyUI/resolve/main/split_files/text_encoders/${COMFYUI_TEXT_ENCODER_FILE:-qwen_2.5_vl_7b_fp8_scaled.safetensors}) &&
+        (test -f /storage/models/vae/${COMFYUI_VAE_FILE:-qwen_image_vae.safetensors} &&
+        echo "vae already downloaded, skipping" ||
+        curl -L --fail --create-dirs -o /storage/models/vae/${COMFYUI_VAE_FILE:-qwen_image_vae.safetensors}
+        https://huggingface.co/Comfy-Org/Qwen-Image_ComfyUI/resolve/main/split_files/vae/${COMFYUI_VAE_FILE:-qwen_image_vae.safetensors})
+
   # Local image generation — see issue #38 (wayfinder map). yurisasc's image
   # is gfx1201-tuned specifically (R9700's arch), unlike the official/AMD
   # ComfyUI image which doesn't pin RDNA4 support — see