feat: Add MCP protocol notes and integrate Atmospheric Computing concepts
Adds new notes for the Model Context Protocol (MCP) including an overview and details on the FastMCP framework.
Integrates 'Atmospheric Computing' concepts into existing AT Protocol notes to better describe its philosophy and architecture:
- Introduced 'philosophy' section in atproto/README.md with Atmospheric Computing definition.
- Updated PDS description in atproto/README.md to reflect 'personal cloud' metaphor.
- Enhanced 'why this matters' in atproto/data.md to link to Atmospheric Computing benefits.
- Added blog post source for Atmospheric Computing.