feat: Bulk actions for contacts (#12763)

Introduces APIs and UI for bulk actions in contacts table. The initial
action available will be assign labels

Fixes: #8536 #12253 

## Screens

<img width="1350" height="747" alt="Screenshot 2025-10-29 at 4 05 08 PM"
src="https://github.com/user-attachments/assets/0792dff5-0371-4b2e-bdfb-cd32db773402"
/>
<img width="1345" height="717" alt="Screenshot 2025-10-29 at 4 05 19 PM"
src="https://github.com/user-attachments/assets/ae510404-c6de-4c15-a720-f6d10cdac25b"
/>

---------

Co-authored-by: Muhsin <muhsinkeramam@gmail.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

spec/jobs/contacts/bulk_action_job_spec.rb

@@ -0,0 +1,22 @@
+require 'rails_helper'
+
+RSpec.describe Contacts::BulkActionJob, type: :job do
+  let(:account) { create(:account) }
+  let(:user) { create(:user, account: account) }
+  let(:params) { { 'ids' => [1], 'labels' => { 'add' => ['vip'] } } }
+
+  it 'invokes the bulk action service with account and user' do
+    service_instance = instance_double(Contacts::BulkActionService, perform: true)
+
+    allow(Contacts::BulkActionService).to receive(:new).and_return(service_instance)
+
+    described_class.perform_now(account.id, user.id, params)
+
+    expect(Contacts::BulkActionService).to have_received(:new).with(
+      account: account,
+      user: user,
+      params: params
+    )
+    expect(service_instance).to have_received(:perform)
+  end
+end