Add Qwen 2.1 host setup script and document Shared model paths.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/qwen21.md

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+# Qwen Image 2.1 (engine `qwen21`) — host weights + Comfy graph
+
+## Host paths (this RTX 5080 box)
+
+| Role | Resolved path |
+|---|---|
+| ComfyUI root (Klein / host agent `ComfyUI (1)`) | `C:\Users\ianjm\AppData\Local\Comfy-Desktop\ComfyUI-Installs\ComfyUI (1)\ComfyUI` |
+| Models root (Desktop Shared via `shared_model_paths.yaml`) | `C:\Users\ianjm\AppData\Local\Comfy-Desktop\ComfyUI-Shared\models` |
+
+Weights must land under Shared so every Desktop instance sees them:
+
+- `diffusion_models\qwen-image-2.1-Q8_0.gguf` (~7.59 GiB) — from `abenzerps/Qwen-Image-2.1-Uncensored-GGUF`
+- `text_encoders\qwen3vl_8b_int8_convrot.safetensors` — from `Comfy-Org/Qwen-Image-2.1` (INT8; BF16 8B VL OOMs on 16 GB)
+- `vae\qwen_image_2.1_vae_bf16.safetensors` — from `Comfy-Org/Qwen-Image-2.1` (**not** the old Qwen-Image 1.0 VAE)
+
+Custom node: `custom_nodes\ComfyUI-GGUF` (`UnetLoaderGGUF`). Do not install a second GGUF pack.
+
+## Setup
+
+```powershell
+powershell -ExecutionPolicy Bypass -File scripts\setup-qwen21.ps1
+```
+
+Restart Comfy **only when idle** (`COMFY_CONTROL_URL/status` → `gpu.busy=false`). Confirm `object_info` lists `UnetLoaderGGUF` and the three filenames.
+
+## App
+
+- Engine key: `qwen21` · UI label: **Qwen 2.1**
+- Generate (T2I) only in this build. Edit / Compose / Iterate / Video disable with: “Qwen 2.1 is T2I in this build”.
+- Sampler defaults: euler / simple / cfg **1** / steps **25** · `ModelSamplingAuraFlow` shift **3.1**
+- Default canvas **1024×1024** (aspect 16:9 / 9:16 / 1:1 honored, multiples of 32). Drop to 768 if VRAM errors.
+- No hero / locks / Klein LoRA stack on this engine.
+
+Graph: `server/assets/studio2_qwen21_t2i.json`.