feat: initial ComfyUI workflow templates extension

- 40 workflow templates (text-to-image, image-to-video, image-to-image,
  text-to-music, upscaling, advanced, nsfw)
- Color-coded placeholder preview images using Pillow
- Template-only extension (no custom nodes)
- Preview generation script for future workflow additions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,15 @@
+[project]
+name = "comfyui-extras"
+version = "0.1.0"
+description = "Curated workflow templates for ComfyUI"
+license = {text = "MIT"}
+readme = "README.md"
+requires-python = ">=3.10"
+dependencies = []
+
+[project.urls]
+Repository = "https://github.com/valknar/comfyui-extras"
+
+[tool.comfy]
+PublisherId = "valknar"
+DisplayName = "ComfyUI Extras"