feat: Add self-contained launcher for easy installation

- Add launcher.sh that handles automatic installation, building, and native module rebuilds
- Add install.sh for quick one-line installation from GitHub
- Update README with new installation methods
- Support running from cloned repo or auto-installing to ~/.local/mcp-servers
- Auto-detect platform and rebuild native modules when needed
- Add environment variables for customization (DATA_DIR, MEMORY_KEEPER_INSTALL_DIR, MEMORY_KEEPER_AUTO_UPDATE)

This makes memory-keeper installation as simple as:
curl -fsSL https://raw.githubusercontent.com/mkreyman/mcp-memory-keeper/main/install.sh  < /dev/null |  bash

Author: mkreyman