feat: Add company model and API with tests (#12548)

# Pull Request Template

## Description

* add Company model with validations for name, domain, description and
  avatar
* Add database migration fo
* Implement endpoints for company CRUD operations
* Add optional company relationship for contacts
* Add test for models, controllers, factories and policies
* Add authorization policies restricting delete to admins
* support JSON API responses
Please include a summary of the change and issue(s) fixed. Also, mention
relevant motivation, context, and any dependencies that this change
requires.

Fixes #(cw-5650)

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

Tests are implemented using `RSpec`

```
$ bundle exec rails db:migrate
$ bundle exec rspec spec/models/company_spec.rb spec/controllers/api/v1/accounts/companies_controller_spec.rb
```

## 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
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

db/migrate/20250929105219_create_companies.rb

@@ -0,0 +1,14 @@
+class CreateCompanies < ActiveRecord::Migration[7.1]
+  def change
+    create_table :companies do |t|
+      t.string :name, null: false
+      t.string :domain
+      t.text :description
+      t.references :account, null: false
+
+      t.timestamps
+    end
+    add_index :companies, [:name, :account_id]
+    add_index :companies, [:domain, :account_id]
+  end
+end

db/migrate/20250929132305_add_company_to_contacts.rb

@@ -0,0 +1,5 @@
+class AddCompanyToContacts < ActiveRecord::Migration[7.1]
+  def change
+    add_reference :contacts, :company, null: true
+  end
+end