feat: add Open WebUI Prompt Plus to extensions list and documentation

docs/extensions/index.md

@@ -0,0 +1,22 @@
+---
+title: Extensions
+---
+
+# Extensions
+
+Standalone frontend extensions to supercharge your Open WebUI.
+
+---
+
+## 🚀 Open WebUI Prompt Plus
+
+**An all-in-one prompt management suite for power users.**
+
+[Open WebUI Prompt Plus](https://github.com/Fu-Jie/open-webui-prompt-plus) elevates your experience with:
+
+- **🤖 AI-Powered Prompt Generator**: Turn natural language into structured prompts.
+- **⚡ Quick Insert Panel**: Spotlight-style search (`Cmd/Ctrl + Shift + P`).
+- **📂 Advanced Management**: Dynamic categories, favorites, and usage stats.
+- **📝 Native Variable Support**: Visual form rendering for template variables.
+
+[:fontawesome-brands-github: View on GitHub](https://github.com/Fu-Jie/open-webui-prompt-plus){ .md-button .md-button--primary }