update: add minimax-pdf skill and reorganize pptx-generator references

- Add minimax-pdf skill (CREATE / FILL / REFORMAT workflows)
- Move pptx-generator reference docs into references/ subdirectory
- Update README.md and README_zh.md with new skill entries

README.md

@@ -16,6 +16,8 @@ Development skills for AI coding agents. Plug into your favorite AI coding tool
 | `ios-application-dev` | iOS application development guide covering UIKit, SnapKit, and SwiftUI. Touch targets, safe areas, navigation patterns, Dynamic Type, Dark Mode, accessibility, collection views, and Apple HIG compliance. |
 | `shader-dev` | Comprehensive GLSL shader techniques for creating stunning visual effects — ray marching, SDF modeling, fluid simulation, particle systems, procedural generation, lighting, post-processing, and more. ShaderToy-compatible. |
 | `gif-sticker-maker` | Convert photos (people, pets, objects, logos) into 4 animated GIF stickers with captions. Funko Pop / Pop Mart style, powered by MiniMax Image & Video Generation API. |
+| `minimax-pdf` | Generate, fill, and reformat PDF documents with a token-based design system. CREATE polished PDFs from scratch (15 cover styles), FILL existing form fields, or REFORMAT documents into a new design. Print-ready output with typography and color derived from document type. |
+| `pptx-generator` | Generate, edit, and read PowerPoint presentations. Create from scratch with PptxGenJS (cover, TOC, content, section divider, summary slides), edit existing PPTX via XML workflows, or extract text with markitdown. |
 
 ## Installation