feat: Backend - Companies API endpoint with pagination and search (#12840)

## Description

Adds API endpoint to list companies with pagination, search, and
sorting.

Fixes
https://linear.app/chatwoot/issue/CW-5930/add-backend-routes-to-get-companies-result
Parent issue:
https://linear.app/chatwoot/issue/CW-5928/add-companies-tab-to-dashboard

## Type of change

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

## How Has This Been Tested?

Added comprehensive specs to
`spec/enterprise/controllers/api/v1/accounts/companies_controller_spec.rb`:
- Pagination (25 per page, multiple pages)
- Search by name and domain (case-insensitive)
- Counter cache for contacts_count
- Account scoping
- Authorization

To reproduce:
```bash
bundle exec rspec spec/enterprise/controllers/api/v1/accounts/companies_controller_spec.rb
bundle exec rubocop enterprise/app/controllers/api/v1/accounts/companies_controller.rb
```

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] 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: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>

spec/enterprise/services/contacts/company_association_service_spec.rb

@@ -45,6 +45,25 @@ RSpec.describe Contacts::CompanyAssociationService, type: :service do
         contact.reload
         expect(contact.company).to eq(existing_company)
       end
+
+      it 'increments company contacts_count when associating contact' do
+        # Create contact without email to avoid auto-association
+        contact = create(:contact, email: nil, account: account)
+        # Manually set email to bypass callbacks
+        # rubocop:disable Rails/SkipsModelValidations
+        contact.update_column(:email, 'jane@techcorp.com')
+        # rubocop:enable Rails/SkipsModelValidations
+
+        valid_email_address = instance_double(ValidEmail2::Address, valid?: true, disposable_domain?: false)
+        allow(ValidEmail2::Address).to receive(:new).with('jane@techcorp.com').and_return(valid_email_address)
+        allow(EmailProviderInfo).to receive(:call).with('jane@techcorp.com').and_return(nil)
+
+        service.associate_company_from_email(contact)
+
+        contact.reload
+        expect(contact.company).to be_present
+        expect(contact.company.contacts_count).to eq(1)
+      end
     end
 
     context 'when contact already has a company' do