Token storage improvements and simplification (nspady#41)

* feat: Migrate legacy token storage and enhance token management

- Introduced a migration process for legacy token files to a new secure location, following the XDG Base Directory Specification.
- Updated token storage paths in the README.md to reflect the new structure and added a custom path option via the `GOOGLE_CALENDAR_MCP_TOKEN_PATH` environment variable.
- Enhanced the `TokenManager` class to handle legacy token migration and ensure backward compatibility.
- Updated utility functions to support the new token storage logic and provide clear documentation on token management.

* Update package name to
  @cocal/google-calendar-mcp and streamline
   credential configuration

  - Change package name from @nspady to
  @cocal
  - Bump version to 1.2.0-beta.3
  - Simplify credential configuration to
  use GOOGLE_OAUTH_CREDENTIALS environment
  variable
  - Remove CLI --credentials-file parameter
   support for cleaner interface
  - Update README and workflow files with
  new package name
  - Remove postinstall script

Update README and architecture documentation to include details on re…

…curring events management.

Move ci.yml file to workflow folder