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/builders/v2/report_builder_spec.rb

@@ -16,7 +16,9 @@ describe V2::ReportBuilder do
         create(:inbox_member, user: user, inbox: inbox)
 
         gravatar_url = 'https://www.gravatar.com'
+        favicon_url = 'https://www.google.com/s2/favicons'
         stub_request(:get, /#{gravatar_url}.*/).to_return(status: 404)
+        stub_request(:get, /#{Regexp.escape(favicon_url)}.*/).to_return(status: 404)
 
         perform_enqueued_jobs do
           10.times do