docs: add OOpenWebUI official newsletter featured recognition to Smart Mind Map, Markdown Normalizer, and Prompt Plus (#52)

* Initial plan

* docs: add OpenWebUI official newsletter featured recognition

- Add newsletter featured callout to Smart Mind Map README.md, README_CN.md, and docs
- Add newsletter featured callout to Markdown Normalizer README.md, README_CN.md, and docs
- Add newsletter featured badge to Prompt Plus in root README.md and README_CN.md
- Reference both newsletters: Jan 28, 2026 and Feb 3, 2026

Co-authored-by: Fu-Jie <33599649+Fu-Jie@users.noreply.github.com>

* docs: fix newsletter links to match actual featured issue per plugin

- Smart Mind Map: link only to Feb 3, 2026 (second newsletter)
- Markdown Normalizer: link only to Jan 28, 2026 (first newsletter)
- Prompt Plus (root READMEs): already correct, no change needed

Co-authored-by: Fu-Jie <33599649+Fu-Jie@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Fu-Jie <33599649+Fu-Jie@users.noreply.github.com>

README.md

@@ -117,7 +117,7 @@ System Prompts are managed in the `docs/prompts/` directory:
 
 Standalone frontend extensions to supercharge your Open WebUI:
 
-- **[Open WebUI Prompt Plus](https://github.com/Fu-Jie/open-webui-prompt-plus)**: An all-in-one prompt management suite featuring AI-powered prompt generation, spotlight-style quick search, and advanced category organization.
+- **[Open WebUI Prompt Plus](https://github.com/Fu-Jie/open-webui-prompt-plus)** [![Newsletter](https://img.shields.io/badge/OpenWebUI_Newsletter-Featured-blue?style=flat-square)](https://openwebui.com/blog/newsletter-january-28-2026): An all-in-one prompt management suite featuring AI-powered prompt generation, spotlight-style quick search, and advanced category organization.
 
 ## 📖 Documentation