Simplify helper methods by using Repository::Owner consistently

[Claude]

Addresses feedback on #96 to simplify the helper methods in application_helper.rb that were handling multiple data type variations (User models, Data objects, and hashes) with complex conditional branching.

Changes

• image_link_to_github_url: Reduced multi-branch conditional to simple ternary operator
• avatar_image_tag: Eliminated middle respond_to?(:login) branch, now handles only User vs. owner objects
• image_link_to_github_url_from_event: Creates Repository::Owner Data object instead of passing hash

Result

Before:

def image_link_to_github_url(user, size = '30x30')
  username = if user.is_a?(User)
    user.username
  elsif user.respond_to?(:login)
    user.login
  else
    user['login']
  end
  link_to avatar_image_tag(user, size), github_url(username)
end

After:

def image_link_to_github_url(user, size = '30x30')
  username = user.is_a?(User) ? user.username : user.login
  link_to avatar_image_tag(user, size), github_url(username)
end

Type consistency enforced: all owner data now uses Repository::Owner Data objects with .login and .avatar_url methods.