feat: Add company auto-association for contacts (CW-5726 Part 2) (#12711)

## Description

Implements real-time company auto-association for contacts based on
email domains. This is **Part 2** of the company model production
rollout (CW-5726).

**Task:**
- When a contact is created with a business email, automatically create
and associate a company from the email domain
- When a contact is updated with an email for the first time (email was
previously nil), associate with a company
- Preserve existing company associations when email changes to avoid
user confusion
- Skip free email providers and disposable domains

**Dependencies:**
⚠️ Requires PR #12657 (Part 1: Backfill migration) to be merged first

**Linear ticket:**
[CW-5726](https://linear.app/chatwoot/issue/CW-5726/company-model-setting-it-up-on-production)

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- Service specs: Tests business email detection, company creation,
association logic, edge cases (existing companies, free emails, nil
emails)
- Integration specs: Tests full callback flow for contact create/update
scenarios
- All tests passing: 10 examples, 0 failures
- RuboCop: 0 offenses

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules (PR #12657 pending)

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>

enterprise/app/services/contacts/company_association_service.rb

@@ -0,0 +1,46 @@
+class Contacts::CompanyAssociationService
+  def associate_company_from_email(contact)
+    return nil if skip_association?(contact)
+
+    company = find_or_create_company(contact)
+    # rubocop:disable Rails/SkipsModelValidations
+    # Intentionally using update_column here to:
+    # 1. Avoid triggering callbacks
+    # 2. Improve performance (We're only setting company_id, no need for validation)
+    contact.update_column(:company_id, company.id) if company
+    # rubocop:enable Rails/SkipsModelValidations
+    company
+  end
+
+  private
+
+  def skip_association?(contact)
+    return true if contact.company_id.present?
+    return true if contact.email.blank?
+
+    detector = Companies::BusinessEmailDetectorService.new(contact.email)
+    return true unless detector.perform
+
+    false
+  end
+
+  def find_or_create_company(contact)
+    domain = extract_domain(contact.email)
+    company_name = derive_company_name(contact, domain)
+
+    Company.find_or_create_by!(account: contact.account, domain: domain) do |company|
+      company.name = company_name
+    end
+  rescue ActiveRecord::RecordNotUnique
+    # If another process created it first, just find that
+    Company.find_by(account: contact.account, domain: domain)
+  end
+
+  def extract_domain(email)
+    email.split('@').last&.downcase
+  end
+
+  def derive_company_name(contact, domain)
+    contact.additional_attributes&.dig('company_name') || domain.split('.').first.tr('-_', ' ').titleize
+  end
+end