Publish May 2026 Newsletter (#2787)

* docs: add May 2026 newsletter

Publish the May 2026 newsletter documenting project milestones including:
- Crossing 100K GitHub stars and top-100 GitHub project status
- 100+ community extensions in catalog
- Fourteen releases (v0.8.4–v0.8.17)
- Multi-agent install support and constitution governance features
- Open Source Friday livestream and media coverage across 25+ languages
- Industry analyst recognition

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: mnriem