Add channel field to ticket creation endpoints

Add a new `channel` field to ticket creation and conversion endpoints in the unstable API spec. The channel field:
- Accepts enum value "email" (currently the only supported value)
- Only supported for customer ticket types
- Defaults to "messenger" when not provided
- Included in ticket response schema with both "email" and "messenger" enum values

Updated schemas:
- create_ticket_request
- convert_conversation_to_ticket_request
- ticket (response schema)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: VarshSuresh

descriptions/0/api.intercom.io.yaml

@@ -13589,6 +13589,7 @@ paths:
                       has_more: false
                     category: Back-office
                     is_shared: false
+                    channel: email
               schema:
                 "$ref": "#/components/schemas/ticket"
         '401':
@@ -13626,6 +13627,7 @@ paths:
                   ticket_attributes:
                     _default_title_: example
                     _default_description_: there is a problem
+                  channel: email
   "/tickets/enqueue":
     post:
       summary: Enqueue create ticket
@@ -13659,6 +13661,7 @@ paths:
                   ticket_attributes:
                     _default_title_: example
                     _default_description_: there is a problem
+                  channel: email
       responses:
         '200':
           description: Successful response
@@ -18186,6 +18189,12 @@ components:
           description: The ID of the type of ticket you want to convert the conversation
             to
           example: '1234'
+        channel:
+          type: string
+          description: The channel for the ticket. Only supported for customer ticket types. Defaults to messenger if not provided.
+          enum:
+          - email
+          example: email
         attributes:
           "$ref": "#/components/schemas/ticket_request_custom_attributes"
       required:
@@ -19053,6 +19062,12 @@ components:
               description: The ID of the team to which the ticket is assigned.
                 If not provided, the ticket will be unassigned.
               example: '8'
+        channel:
+          type: string
+          description: The channel for the ticket. Only supported for customer ticket types. Defaults to messenger if not provided.
+          enum:
+          - email
+          example: email
       required:
       - ticket_type_id
       - contacts
@@ -22007,6 +22022,13 @@ components:
           - Back-office
           - Tracker
           example: Customer
+        channel:
+          type: string
+          description: The channel for the ticket. Only supported for customer ticket types.
+          enum:
+          - email
+          - messenger
+          example: messenger
         ticket_attributes:
           "$ref": "#/components/schemas/ticket_custom_attributes"
         ticket_state: