feat: Add raw GraphQL query command

[mattatcha]

Summary

Adds linearis graphql command for executing custom GraphQL queries against the Linear API.

Usage

# Inline query
linearis graphql '{ viewer { id name } }'

# From file
linearis graphql --file query.graphql

# With variables
linearis graphql 'query($id: String!) { issue(id: $id) { title } }' --vars '{"id": "uuid"}'

# From stdin
echo '{ viewer { id } }' | linearis graphql

Closes #31

[iamfj]

Thanks for adding the raw GraphQL command, @mattatcha!

Since this was opened, the project went through a complete architecture rewrite (#49) with a new five-layer design and GraphQL codegen. This PR is no longer compatible with the current structure.

Closing this PR, but the feature request in #31 is still open. The new architecture actually makes this kind of feature easier to add — if you're interested in picking it back up, check out the current patterns in AGENTS.md.

Thanks for contributing! 🙏