feat(#23): implement mosaic-plugin-brain skill

- Add brain skill for Ideas/Brain API integration
- Quick capture for brain dumps
- Semantic search and query capabilities
- Full CRUD operations on ideas
- Tag management and filtering
- Shell script CLI with colored output
- Comprehensive documentation (SKILL.md, README.md)
- Configuration via env vars or ~/.config/mosaic/brain.conf

packages/skills/brain/.env.example

@@ -0,0 +1,11 @@
+# Mosaic Brain Configuration Example
+# Copy to ~/.config/mosaic/brain.conf and fill in your values
+
+# Mosaic Stack API URL
+MOSAIC_API_URL=http://localhost:3001
+
+# Your workspace UUID (get from Mosaic Stack web app)
+MOSAIC_WORKSPACE_ID=
+
+# Your API authentication token (get from Mosaic Stack settings)
+MOSAIC_API_TOKEN=