feat(runtime): add Ruby provider

[CalvinAllen]

Add Ruby runtime provider to dtvem for managing Ruby versions.

Current State

Empty directory exists at src/runtimes/ruby/ but no implementation.

Remaining Work

Core Implementation

• Create src/runtimes/ruby/provider.go with all 19 Provider interface methods
• Add init() function for auto-registration: runtime.Register(NewProvider())
• Import in src/main.go: _ "github.com/CodingWithCalvin/dtvem/src/runtimes/ruby"
• Update schemas/runtimes.schema.json to add "ruby" to runtime enum

Provider Methods

• Implement Shims() to return: ["ruby", "gem", "irb", "bundle", "rake", "rdoc", "ri"]
• Implement ShouldReshimAfter() for gem install/uninstall and bundle install/update
• Implement version listing from ruby-lang.org
• Implement download/installation logic (platform-specific)
• Implement migration detection for rbenv, rvm, chruby, system

Testing & Documentation

• Add tests using provider contract harness
• Update documentation with Ruby examples

Version Sources

• Official: https://www.ruby-lang.org/en/downloads/
• Windows: RubyInstaller (https://rubyinstaller.org/)

Migration Sources

• rbenv: ~/.rbenv/versions/
• rvm: ~/.rvm/rubies/
• chruby: /opt/rubies/ or ~/.rubies/

References

• Provider interface: src/internal/runtime/provider.go
• Example implementations: src/runtimes/node/, src/runtimes/python/