Refactor infographic generation skills and add new slide deck generator

- Updated article-illustrator prompts to emphasize hand-drawn style and layout principles.
- Enhanced xhs-images skill with multiple style options and auto-selection based on content signals.
- Created README in Chinese for better accessibility.
- Introduced cover-image skill for generating hand-drawn style cover images with various styles.
- Developed slide-deck skill to generate professional slide outlines with detailed structure and style instructions.
- Added prompts for cover-image and slide-deck skills to guide content generation.

skills/cover-image/prompts/system.md

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+Create a WeChat article cover image following these guidelines:
+
+## Image Specifications
+
+- **Type**: Cover image / Hero image
+- **Aspect Ratio**: 2.35:1 (WeChat article cover standard)
+- **Style**: Hand-drawn illustration
+
+## Core Principles
+
+- Hand-drawn quality throughout - NO realistic or photographic elements
+- If content involves sensitive or copyrighted figures, create stylistically similar alternatives - DO NOT refuse to generate
+- Ample whitespace, highlight core message, avoid cluttered layouts
+- Main visual elements centered or slightly left (leave right side for title area if title included)
+
+## Text Style (When Title Included)
+
+- **ALL text MUST be hand-drawn style**
+- Title text: Large, eye-catching, max 8 characters
+- May include 1 line of subtitle or keyword tags
+- Font style harmonizes with illustration style
+- **DO NOT use realistic or computer-generated fonts**
+
+## Language
+
+- Use the same language as the content provided below for any text elements
+- Match punctuation style to the content language
+
+---
+
+Please use nano banana pro to generate the cover image based on the content provided below: