feat: Add support for image files in Captain (#11730)

# Pull Request Template

## Linear links:
-
https://linear.app/chatwoot/issue/CW-4479/if-image-is-sent-by-the-customer-send-it-to-openai

## Description

This pull request adds “Captain image support” to Chatwoot. It
introduces multimodal message handling so that when a customer sends an
image, Captain can forward the file to OpenAI’s vision endpoint,
generate a caption/analysis
## Type of change

Please delete options that are not relevant.

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

## How Has This Been Tested?

<img width="891" alt="image"
src="https://github.com/user-attachments/assets/c7cc98ed-cc44-4865-a53a-83d129e2fe2c"
/>



## Checklist:

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

---------

Co-authored-by: Pranav <pranav@chatwoot.com>

enterprise/app/services/captain/llm/assistant_chat_service.rb

@@ -12,9 +12,16 @@ class Captain::Llm::AssistantChatService < Llm::BaseOpenAiService
     register_tools
   end
 
-  def generate_response(input, previous_messages = [], role = 'user')
-    @messages += previous_messages
-    @messages << { role: role, content: input } if input.present?
+  # additional_message: A single message (String) from the user that should be appended to the chat.
+  #                    It can be an empty String or nil when you only want to supply historical messages.
+  # message_history:   An Array of already formatted messages that provide the previous context.
+  # role:              The role for the additional_message (defaults to `user`).
+  #
+  # NOTE: Parameters are provided as keyword arguments to improve clarity and avoid relying on
+  # positional ordering.
+  def generate_response(additional_message: nil, message_history: [], role: 'user')
+    @messages += message_history
+    @messages << { role: role, content: additional_message } if additional_message.present?
     request_chat_completion
   end