feat: Add company backfill migration for existing contacts (Part 1) (#12657)

## Description

Implements company backfill migration infrastructure for existing
contacts. This is **Part 1 of 2** for the company model production
rollout as described in
[CW-5726](https://linear.app/chatwoot/issue/CW-5726/company-model-setting-it-up-on-production).

Creates jobs and services to associate existing contacts with companies
based on their email domains, filtering out free email providers (gmail,
yahoo, etc.) and disposable addresses.
 

**What's included:**
- Business email detector service with ValidEmail2 (uses
`disposable_domain?` to avoid DNS lookups)
- Per-account batch job to process contacts for one account
- Orchestrator job to iterate all accounts
- Rake task: `bundle exec rake companies:backfill`

~~*NOTE*: I'm using a hard-coded approach to determine if something is a
"business" email by filtering out emails that are usually personal. I've
also added domains that are common to some of our customers' regions.
This should be simpler. I looked into `Valid_Email2` and I couldn't find
anything to dictate whether an email is a personal email or a business
one. I don't think the approach used in the frontend is valid here.~~
UPDATE: Using `email_provider_info` gem instead.


**Pending - Part 2 (separate PR):** Real-time company creation for new
contacts

## Type of change

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

## How Has This Been Tested?

```bash
# Run all new tests
bundle exec rspec spec/enterprise/services/companies/business_email_detector_service_spec.rb \\
                   spec/enterprise/jobs/migration/company_account_batch_job_spec.rb \\
                   spec/enterprise/jobs/migration/company_backfill_job_spec.rb

# Run RuboCop
bundle exec rubocop enterprise/app/services/companies/business_email_detector_service.rb \\
                     enterprise/app/jobs/migration/company_account_batch_job.rb \\
                     enterprise/app/jobs/migration/company_backfill_job.rb \\
                     lib/tasks/companies.rake
```

**Performance optimization:**
- Uses `disposable_domain?` instead of `disposable?` to avoid DNS MX
lookups (discovered via tcpdump analysis - `disposable?` was making
network calls for every email, causing 100x slowdown)

## 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
- [ ] I have made corresponding changes to the documentation
- [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

---------

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

spec/enterprise/services/companies/business_email_detector_service_spec.rb

@@ -0,0 +1,99 @@
+require 'rails_helper'
+
+RSpec.describe Companies::BusinessEmailDetectorService, type: :service do
+  let(:service) { described_class.new(email) }
+
+  describe '#perform' do
+    context 'when email is from a business domain' do
+      let(:email) { 'user@acme.com' }
+      let(:valid_email_address) { instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false) }
+
+      before do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with(email).and_return(nil)
+      end
+
+      it 'returns true' do
+        expect(service.perform).to be(true)
+      end
+    end
+
+    context 'when email is from gmail' do
+      let(:email) { 'user@gmail.com' }
+      let(:valid_email_address) { instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false) }
+
+      before do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with(email).and_return('gmail')
+      end
+
+      it 'returns false' do
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email is from Brazilian free provider' do
+      let(:email) { 'user@uol.com.br' }
+      let(:valid_email_address) { instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false) }
+
+      before do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with(email).and_return('uol')
+      end
+
+      it 'returns false' do
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email is disposable' do
+      let(:email) { 'user@mailinator.com' }
+      let(:disposable_email_address) { instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: true) }
+
+      it 'returns false' do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(disposable_email_address)
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email is invalid format' do
+      let(:email) { 'invalid-email' }
+      let(:invalid_email_address) { instance_double(ValidEmail2::Address, valid?: false) }
+
+      it 'returns false' do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(invalid_email_address)
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email is nil' do
+      let(:email) { nil }
+
+      it 'remains false' do
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email is empty string' do
+      let(:email) { '' }
+
+      it 'returns false' do
+        expect(service.perform).to be(false)
+      end
+    end
+
+    context 'when email domain is uppercase' do
+      let(:email) { 'user@GMAIL.COM' }
+      let(:valid_email_address) { instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false) }
+
+      before do
+        allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with(email).and_return('gmail')
+      end
+
+      it 'returns false (case insensitive)' do
+        expect(service.perform).to be(false)
+      end
+    end
+  end
+end