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>

enterprise/app/models/company.rb

@@ -2,13 +2,14 @@
 #
 # Table name: companies
 #
-#  id          :bigint           not null, primary key
-#  description :text
-#  domain      :string
-#  name        :string           not null
-#  created_at  :datetime         not null
-#  updated_at  :datetime         not null
-#  account_id  :bigint           not null
+#  id             :bigint           not null, primary key
+#  contacts_count :integer
+#  description    :text
+#  domain         :string
+#  name           :string           not null
+#  created_at     :datetime         not null
+#  updated_at     :datetime         not null
+#  account_id     :bigint           not null
 #
 # Indexes
 #
@@ -31,4 +32,7 @@ class Company < ApplicationRecord
   has_many :contacts, dependent: :nullify
 
   scope :ordered_by_name, -> { order(:name) }
+  scope :search_by_name_or_domain, lambda { |query|
+    where('name ILIKE :search OR domain ILIKE :search', search: "%#{query.strip}%")
+  }
 end

enterprise/app/models/enterprise/concerns/contact.rb

@@ -1,7 +1,7 @@
 module Enterprise::Concerns::Contact
   extend ActiveSupport::Concern
   included do
-    belongs_to :company, optional: true
+    belongs_to :company, optional: true, counter_cache: true
 
     after_commit :associate_company_from_email,
                  on: [:create, :update],