Add brain-os to Claude Plugins

[9fw2pq8sgb-art]

Adds brain-os to the 🔌 Claude Plugins section.

A developer-focused Claude Code plugin that turns Obsidian into a second brain that knows your code, not just notes:

• Project-aware sessions — a SessionStart hook makes Claude aware of your projects and their linked code repos.
• Code architecture in your vault — graphify maps a repo into named feature-clusters + diagrams, deposited next to your notes.
• Unified local semantic search (qmd) over notes and code maps.

Local-first, MIT, one /brain-setup. Repo: https://github.com/9fw2pq8sgb-art/obsidian-brain-os

Verify: /plugin marketplace add 9fw2pq8sgb-art/obsidian-brain-os → /plugin install brain-os@obsidian-brain-os → /brain-setup.