feat: Add infinite scroll to contacts search page (#13376)

## Summary
- Add `has_more` to contacts search API response to enable infinite
scroll without expensive count queries
- Set `count` to the number of items in the current page instead of
total count
- Implement "Load more" button for contacts search results
- Keep existing contacts visible while loading additional pages

## Changes

### Backend
- Add `fetch_contacts_with_has_more` method that fetches N+1 records to
determine if more pages exist
- Return `has_more` in search endpoint meta response
- Set `count` to current page size instead of total count

### Frontend
- Add `APPEND_CONTACTS` mutation for appending contacts without clearing
existing ones
- Update search action to support `append` parameter
- Add `ContactsLoadMore` component with loading state
- Update `ContactsListLayout` to support infinite scroll mode
- Update `ContactsIndex` to use infinite scroll for search view

app/controllers/api/v1/accounts/contacts_controller.rb

@@ -28,8 +28,7 @@ class Api::V1::Accounts::ContactsController < Api::V1::Accounts::BaseController
       'name ILIKE :search OR email ILIKE :search OR phone_number ILIKE :search OR contacts.identifier LIKE :search',
       search: "%#{params[:q].strip}%"
     )
-    @contacts = fetch_contacts(contacts)
-    @contacts_count = @contacts.total_count
+    @contacts = fetch_contacts_with_has_more(contacts)
   end
 
   def import
@@ -142,6 +141,24 @@ class Api::V1::Accounts::ContactsController < Api::V1::Accounts::BaseController
       .per(RESULTS_PER_PAGE)
   end
 
+  def fetch_contacts_with_has_more(contacts)
+    includes_hash = { avatar_attachment: [:blob] }
+    includes_hash[:contact_inboxes] = { inbox: :channel } if @include_contact_inboxes
+
+    # Calculate offset manually to fetch one extra record for has_more check
+    offset = (@current_page.to_i - 1) * RESULTS_PER_PAGE
+    results = filtrate(contacts)
+              .includes(includes_hash)
+              .offset(offset)
+              .limit(RESULTS_PER_PAGE + 1)
+              .to_a
+
+    @has_more = results.size > RESULTS_PER_PAGE
+    results = results.first(RESULTS_PER_PAGE) if @has_more
+    @contacts_count = results.size
+    results
+  end
+
   def build_contact_inbox
     return if params[:inbox_id].blank?