Fix namespace resolution for Foo::Bar lookups

[Copilot]

Namespace scope resolution was broken for references like Foo::Bar.class_method - it would search for Bar instead of the full path Foo::Bar, returning incorrect or missing definitions.

Changes

• lib/ruby_language_server/project_manager.rb: Modified possible_definitions to build scope paths from the leftmost continuous chain of class/module names rather than just the rightmost index

  # Before: For Foo::Bar.method, built scope path ['Bar']
  # After:  For Foo::Bar.method, builds scope path ['Foo', 'Bar']
  
  # Find continuous chain ending at rightmost class
  leftmost_continuous_index = rightmost_class_index
  class_module_indices.reverse.each_cons(2) do |right, left|
    break unless right == left + 1
    leftmost_continuous_index = left
  end
  scope_path_parts = context[leftmost_continuous_index..-2]

• spec/lib/ruby_language_server/project_manager_spec.rb: Added tests for Foo::Bar class lookup and Foo::Bar.class_method method lookup

• Dockerfile: Switched from ruby:4.0-alpine to ruby:4.0-slim to resolve Alpine repository TLS errors blocking CI

Original prompt

---

This section details on the original issue you should resolve

<issue_title>When looking for Foo::Bar it should find Bar inside of Foo</issue_title>
<issue_description>It seems like this functionality broke at some point recently.

For example:

module Foo
  class Bar
    def self.class_method
    end
    def some_method
    end
  end
end

Foo::Bar # clicking on Bar should find the class
Foo::Bar.class_method # clicking on class_method should find the method
```</issue_description>

<agent_instructions>Write a couple of tests first - based on the comments in the code block.  Then fix the issue.
I suspect this was broken recently - so look at recent scope finding changes.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes When looking for Foo::Bar it should find Bar inside of Foo #136

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.