feat: captain channel type langfuse metadata (#13574)

# Pull Request Template

## Description

Adds channel type to Captain assistant traces in Langfuse

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. Please also list any relevant details
for your test configuration.

<img width="906" height="672" alt="image"
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## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

spec/enterprise/services/captain/assistant/agent_runner_service_spec.rb

@@ -278,6 +278,7 @@ RSpec.describe Captain::Assistant::AgentRunnerService do
         contact_id: contact.id,
         status: conversation.status
       )
+      expect(state[:channel_type]).to eq(inbox.channel_type)
     end
 
     it 'includes contact attributes when contact is present' do