add EXTEND.md configuration support

skills/baoyu-image-gen/references/config/preferences-schema.md

@@ -0,0 +1,66 @@
+---
+name: preferences-schema
+description: EXTEND.md YAML schema for baoyu-image-gen user preferences
+---
+
+# Preferences Schema
+
+## Full Schema
+
+```yaml
+---
+version: 1
+
+default_provider: null      # google|openai|dashscope|null (null = auto-detect)
+
+default_quality: null       # normal|2k|null (null = use default: 2k)
+
+default_aspect_ratio: null  # "16:9"|"1:1"|"4:3"|"3:4"|"2.35:1"|null
+
+default_image_size: null    # 1K|2K|4K|null (Google only, overrides quality)
+
+default_model:
+  google: null              # e.g., "gemini-3-pro-image-preview"
+  openai: null              # e.g., "gpt-image-1.5"
+  dashscope: null           # e.g., "z-image-turbo"
+---
+```
+
+## Field Reference
+
+| Field | Type | Default | Description |
+|-------|------|---------|-------------|
+| `version` | int | 1 | Schema version |
+| `default_provider` | string\|null | null | Default provider (null = auto-detect) |
+| `default_quality` | string\|null | null | Default quality (null = 2k) |
+| `default_aspect_ratio` | string\|null | null | Default aspect ratio |
+| `default_image_size` | string\|null | null | Google image size (overrides quality) |
+| `default_model.google` | string\|null | null | Google default model |
+| `default_model.openai` | string\|null | null | OpenAI default model |
+| `default_model.dashscope` | string\|null | null | DashScope default model |
+
+## Examples
+
+**Minimal**:
+```yaml
+---
+version: 1
+default_provider: google
+default_quality: 2k
+---
+```
+
+**Full**:
+```yaml
+---
+version: 1
+default_provider: google
+default_quality: 2k
+default_aspect_ratio: "16:9"
+default_image_size: 2K
+default_model:
+  google: "gemini-3-pro-image-preview"
+  openai: "gpt-image-1.5"
+  dashscope: "z-image-turbo"
+---
+```