refactor: rebrand to KERNL - The Core Intelligence Layer

BREAKING CHANGE: Rebranding from Project Mind to KERNL

- Updated all documentation (20+ files)
- Renamed directory: project-mind-mcp → kernl-mcp
- Updated package namespace: @project-mind → @kernl
- Updated API calls: pm.* → kernl.*
- Deleted old logo files
- Updated to v2.0.0 with multi-platform strategy
- Added conversation export as priority feature

KERNL now supports:
- Claude (Anthropic MCP) - v2.0.0 in development
- ChatGPT (OpenAI Actions) - Q1 2026
- Gemini (Google Extensions) - Q2 2026
- Grok (xAI API) - Q2 2026
- DeepSeek (API) - Q2 2026
- Ollama (Local) - Q2 2026

Tagline: The Core Intelligence Layer for AI Systems