Exclude CI/dev files from built gem and update homepage

[ahaverbuch]

Summary

• Filter .buildkite/pipeline.yml, Dockerfile, docker-compose.yml, and solano.yml out of spec.files so they don't ship in the published gem
• Update spec.homepage to point at the current repo (gusto/fixy) instead of the original chetane/fixy

Test plan

• gem build fixy.gemspec and inspect the resulting .gem to confirm excluded files are absent and lib/, README, CHANGELOG, LICENSE, Rakefile, Gemfile remain

[corsonknowles]

This is fine as it's current/more accurate about who and how to contact about this fork, but I would suggest moving info about the Fork into either the Description or Summary.

Alternatively, since it's an array, you could use both entries

[ahaverbuch]

Yeah, Omar isn't here anymore so this gives more accurate