docs(api): add contact merge endpoint to swagger documentation

Add API documentation for POST /api/v1/accounts/{account_id}/actions/contact_merge

This endpoint allows merging two contacts, where the base contact survives
and receives all data from the mergee contact.

Closes chatwoot/docs#243

swagger/paths/application/contacts/merge.yml

@@ -0,0 +1,56 @@
+post:
+  tags:
+    - Contacts
+  operationId: contactMerge
+  summary: Merge Contacts
+  security:
+    - userApiKey: []
+  description: |
+    Merge two contacts into one. The base contact survives and receives all data
+    from the mergee contact. The mergee contact is permanently deleted after the merge.
+
+    This operation is irreversible. All conversations, labels, and custom attributes
+    from the mergee contact will be transferred to the base contact.
+  requestBody:
+    required: true
+    content:
+      application/json:
+        schema:
+          type: object
+          required:
+            - base_contact_id
+            - mergee_contact_id
+          properties:
+            base_contact_id:
+              type: integer
+              description: ID of the contact that will survive the merge and receive all data
+              example: 1
+            mergee_contact_id:
+              type: integer
+              description: ID of the contact that will be merged into the base contact and deleted
+              example: 2
+  responses:
+    '200':
+      description: Contacts merged successfully
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/contact_base'
+    '400':
+      description: Bad request - invalid contact IDs or contacts cannot be merged
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/bad_request_error'
+    '401':
+      description: Unauthorized
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/bad_request_error'
+    '404':
+      description: One or both contacts not found
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/bad_request_error'

swagger/paths/index.yml

@@ -275,6 +275,12 @@
 /api/v1/accounts/{account_id}/contacts/{id}/contactable_inboxes:
   $ref: ./application/contactable_inboxes/get.yml
 
+# Contact Merge
+/api/v1/accounts/{account_id}/actions/contact_merge:
+  parameters:
+    - $ref: '#/components/parameters/account_id'
+  post:
+    $ref: ./application/contacts/merge.yml
 
 # Automation Rule
 /api/v1/accounts/{account_id}/automation_rules: