`gem build mcp.gemspec` outputs the built gem into the working directory (e.g. mcp-0.7.1.gem)
rather than pkg/, which is already ignored.
Without this entry, the file shows up as an untracked file and risks being accidentally
staged and committed during release preparation or local development.
RubyGems may be used across a wide range of Ruby versions,
from the minimum supported version to development versions.
To allow local development with any Ruby version,
the Ruby version is not locked using a `.ruby-version` file.
This enables developers to work with their preferred Ruby version and
frees repository maintainers from the need to update `.ruby-version`.
Additionally, because testing against supported Ruby versions is performed
in CI before release, the version in `.ruby-version` is not important.
