feat: Add automatic favicon fetching for companies (#13013)

## Summary

This Enterprise-only feature automatically fetches a favicon for
companies created with a domain, and adds a batch task to backfill
missing avatars for existing companies. The flow only targets companies
that do not already have an attached avatar, so existing avatars are
left untouched.


## Demo 



https://github.com/user-attachments/assets/d050334e-769f-4e46-b6e7-f7423727a192



## What changed

- Added `Avatar::AvatarFromFaviconJob` to build a Google favicon URL
from the company domain and fetch it through `Avatar::AvatarFromUrlJob`
- Triggered favicon fetching from `Company` with `after_create_commit`
- Added `Companies::FetchAvatarsJob` to batch existing companies that
are missing avatars
- Added `companies:fetch_missing_avatars` under `enterprise/lib/tasks`
- Kept the company-specific implementation inside the Enterprise
boundary
- Stubbed the new favicon request in unrelated specs that now hit this
callback indirectly
- Updated a couple of CI-sensitive specs that were failing due to
callback side effects / reload-safe exception assertions

## How to verify

1. Create a company in Enterprise with a valid domain and no avatar.
2. Confirm that a favicon-based avatar gets attached shortly after
creation.
3. Create another company with a domain and an avatar already attached.
4. Confirm that the existing avatar is not replaced.
5. Run `companies:fetch_missing_avatars`.
6. Confirm that existing companies without avatars get one, while
companies that already have avatars remain unchanged.

## Notes

- This change does not refresh or overwrite existing company avatars
- Favicon fetching only runs for companies with a present domain
- The branch includes the latest `develop`

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>

spec/enterprise/models/conversation_spec.rb

@@ -6,9 +6,14 @@ RSpec.describe Conversation, type: :model do
   end
 
   describe 'SLA policy updates' do
-    let!(:conversation) { create(:conversation) }
+    let(:conversation) { create(:conversation) }
     let!(:sla_policy) { create(:sla_policy, account: conversation.account) }
 
+    before do
+      stub_request(:get, %r{\Ahttps://www\.gravatar\.com.*}).to_return(status: 404)
+      stub_request(:get, %r{\Ahttps://www\.google\.com/s2/favicons.*}).to_return(status: 404)
+    end
+
     it 'generates an activity message when the SLA policy is updated' do
       conversation.update!(sla_policy_id: sla_policy.id)