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>

spec/enterprise/services/contacts/company_association_service_spec.rb

@@ -0,0 +1,83 @@
+require 'rails_helper'
+
+RSpec.describe Contacts::CompanyAssociationService, type: :service do
+  let(:account) { create(:account) }
+  let(:service) { described_class.new }
+
+  describe '#associate_company_from_email' do
+    context 'when contact has business email and no company' do
+      it 'creates a new company and associates it' do
+        contact = create(:contact, email: 'john@acme.com', account: account, company_id: nil)
+        Company.delete_all # Delete any companies created by the callback
+        # rubocop:disable Rails/SkipsModelValidations
+        contact.update_column(:company_id, nil) # Delete the company association created by the callback
+        # rubocop:enable Rails/SkipsModelValidations
+
+        valid_email_address = instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false)
+        allow(ValidEmail2::Address).to receive(:new).with('john@acme.com').and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with('john@acme.com').and_return(nil)
+
+        expect do
+          service.associate_company_from_email(contact)
+        end.to change(Company, :count).by(1)
+
+        contact.reload
+        expect(contact.company).to be_present
+        expect(contact.company.domain).to eq('acme.com')
+        expect(contact.company.name).to eq('Acme')
+      end
+
+      it 'reuses existing company with same domain' do
+        existing_company = create(:company, domain: 'acme.com', account: account)
+        contact = create(:contact, email: 'john@acme.com', account: account, company_id: nil)
+        # rubocop:disable Rails/SkipsModelValidations
+        contact.update_column(:company_id, nil) # Delete the company association created by the callback
+        # rubocop:enable Rails/SkipsModelValidations
+
+        valid_email_address = instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false)
+        allow(ValidEmail2::Address).to receive(:new).with('john@acme.com').and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with('john@acme.com').and_return(nil)
+
+        expect do
+          service.associate_company_from_email(contact)
+        end.not_to change(Company, :count)
+
+        contact.reload
+        expect(contact.company).to eq(existing_company)
+      end
+    end
+
+    context 'when contact already has a company' do
+      it 'skips association and returns nil' do
+        existing_company = create(:company, account: account)
+        contact = create(:contact, email: 'john@acme.com', account: account, company_id: existing_company.id)
+        result = service.associate_company_from_email(contact)
+
+        expect(result).to be_nil
+        contact.reload
+        expect(contact.company).to eq(existing_company)
+      end
+    end
+
+    context 'when contact has free email provider' do
+      it 'skips association for email' do
+        contact = create(:contact, email: 'john@gmail.com', account: account, company_id: nil)
+        expect do
+          service.associate_company_from_email(contact)
+        end.not_to change(Company, :count)
+        contact.reload
+        expect(contact.company).to be_nil
+      end
+    end
+
+    context 'when contact has no email' do
+      it 'skips association' do
+        contact = create(:contact, email: nil, account: account, company_id: nil)
+
+        result = service.associate_company_from_email(contact)
+        expect(result).to be_nil
+        expect(contact.reload.company).to be_nil
+      end
+    end
+  end
+end