feat(skills): add comfyui skill — CLI-driven image/video/audio generation

Agent-friendly ComfyUI skill using the comfyui-skill CLI (invoked via uvx,
no persistent install). The CLI wraps ComfyUI's REST API into named 'skills'
with parameter schemas — the agent works with friendly args like
{"prompt": "a cat"} instead of raw node graphs.

- SKILL.md: setup/onboarding, core workflow, decision tree, multi-server,
  image upload, model/node discovery, queue management, pitfalls
- references/cli-reference.md: complete command map (27 leaf commands)
- references/api-notes.md: underlying REST endpoints for debugging
- scripts/comfyui_setup.sh: workspace initialization

Based on comfyui-skill-cli by HuangYuChuh, original skill work by kshitijk4poor.

optional-skills/creative/comfyui/references/api-notes.md

@@ -0,0 +1,103 @@
+# ComfyUI REST API Notes
+
+The `comfyui-skill` CLI wraps these endpoints. This reference is for debugging,
+understanding errors, or advanced use when the CLI doesn't cover a specific need.
+
+## Endpoints the CLI Uses
+
+| Endpoint | Method | CLI Command |
+|----------|--------|-------------|
+| `/system_stats` | GET | `server status`, `server stats` |
+| `/prompt` | POST | `run`, `submit` |
+| `/history/{prompt_id}` | GET | `status`, `run` (polling) |
+| `/history` | GET | `history list --server` |
+| `/queue` | GET | `queue list` |
+| `/queue` | POST | `queue clear`, `queue delete` |
+| `/interrupt` | POST | `cancel` |
+| `/free` | POST | `free` |
+| `/object_info` | GET | `nodes list`, `workflow import` (schema extraction) |
+| `/object_info/{class}` | GET | `nodes info` |
+| `/models` | GET | `models list` |
+| `/models/{folder}` | GET | `models list <folder>`, `deps check` |
+| `/view` | GET | `run` (output download) |
+| `/upload/image` | POST | `upload` |
+| `/upload/mask` | POST | `upload --mask` |
+| `/node_replacements` | GET | `workflow import` (deprecated node detection) |
+| `/internal/logs/raw` | GET | `logs show` |
+| `/workflow_templates` | GET | `templates list` |
+| `/global_subgraphs` | GET | `templates subgraphs` |
+| `/v2/userdata` | GET | `workflow import --from-server` |
+| `/ws` | WebSocket | `run` (real-time progress) |
+
+### Cloud-specific
+
+| Endpoint | Method | Purpose |
+|----------|--------|---------|
+| `/api/jobs` | GET | Job listing with filtering |
+| `/api/jobs/{id}` | GET | Job details |
+
+### ComfyUI Manager (optional plugin)
+
+| Endpoint | Method | CLI Command |
+|----------|--------|-------------|
+| `/manager/queue/start` | GET | `deps install` |
+| `/manager/queue/install` | POST | `deps install` (custom nodes) |
+| `/manager/queue/install_model` | POST | `deps install --models` |
+| `/manager/queue/status` | GET | `deps install` (progress) |
+
+## Local vs Cloud Differences
+
+| | Local | Cloud |
+|---|---|---|
+| Base URL | `http://127.0.0.1:8188` | `https://cloud.comfy.org` |
+| Route prefix | none | `/api` |
+| Auth | none or bearer token | `X-API-Key` header |
+| Job status | Poll `/history/{id}` | `/api/jobs/{id}` |
+| Output download | Direct bytes from `/view` | 302 redirect → signed URL |
+| WebSocket | `ws://host:port/ws?clientId={uuid}` | `wss://host/ws?clientId={uuid}&token={key}` |
+| Concurrent jobs | Sequential | Tier-limited (Free: 1, Creator: 3, Pro: 5) |
+
+The CLI handles all of these differences transparently based on the server config.
+
+## Workflow JSON Format (API Format)
+
+```json
+{
+  "node_id_string": {
+    "class_type": "NodeClassName",
+    "inputs": {
+      "param_name": "value",
+      "linked_input": ["source_node_id", output_index]
+    }
+  }
+}
+```
+
+- Node IDs are strings (`"3"`, not `3`)
+- Links: `["node_id", output_index]` — 0-based int
+- `class_type` must match exactly (case-sensitive)
+
+## POST /prompt Payload
+
+```json
+{
+  "prompt": { "<workflow>" },
+  "client_id": "uuid",
+  "extra_data": {
+    "api_key_comfy_org": "key-for-paid-api-nodes"
+  }
+}
+```
+
+The CLI constructs this from the imported workflow + injected parameters.
+
+## WebSocket Message Types
+
+| Type | When | Key Fields |
+|------|------|------------|
+| `execution_start` | Prompt begins | `prompt_id` |
+| `executing` | Node running (`null` = done) | `node`, `prompt_id` |
+| `progress` | Sampling steps | `node`, `value`, `max` |
+| `executed` | Node output ready | `node`, `output` |
+| `execution_success` | All nodes done | `prompt_id` |
+| `execution_error` | Failure | `exception_type`, `exception_message` |