feat: Add support for shared post and story attachment types in Instagram messages (#12997)

When users share Instagram posts or stories via DM, Instagram sends
webhooks with type `ig_post` and `ig_story` attachments. The system was
failing on these types because they weren't defined in the file_types.
This PR fixes the issue by handling all shared types and rendering them
on the front end.

**Shared post**

<img width="2154" height="1828" alt="CleanShot 2025-12-03 at 16 29
14@2x"
src="https://github.com/user-attachments/assets/7e731171-4904-43a6-abeb-b1db2c262742"
/>

**Shared status**
<img width="1702" height="1676" alt="CleanShot 2025-12-03 at 16 10
25@2x"
src="https://github.com/user-attachments/assets/6a151233-ce47-429d-b7c2-061514b20e05"
/>


Fixes
https://linear.app/chatwoot/issue/CW-5441/argumenterror-ig-story-is-not-a-valid-file-type-argumenterror

app/models/attachment.rb

@@ -40,7 +40,7 @@ class Attachment < ApplicationRecord
   validate :acceptable_file
   validates :external_url, length: { maximum: Limits::URL_LENGTH_LIMIT }
   enum file_type: { :image => 0, :audio => 1, :video => 2, :file => 3, :location => 4, :fallback => 5, :share => 6, :story_mention => 7,
-                    :contact => 8, :ig_reel => 9, :ig_post => 10 }
+                    :contact => 8, :ig_reel => 9, :ig_post => 10, :ig_story => 11 }
 
   def push_event_data
     return unless file_type