Consolidate single-action controllers into resource controllers

Merge 11 single-action controllers into their parent resource controllers:
- Invoice: send, sendPreview, clone, changeStatus -> InvoicesController
- Estimate: send, sendPreview, clone, convertToInvoice, changeStatus -> EstimatesController
- Payment: send, sendPreview -> PaymentsController

Extract clone and convert business logic from controllers into services:
- InvoiceService: add clone(), changeStatus()
- EstimateService: add clone(), convertToInvoice(), changeStatus()

Previously this logic was inlined in controllers (~80-90 lines each).

tests/Feature/Admin/EstimateTest.php

@@ -1,7 +1,6 @@
 <?php
 
 use App\Http\Controllers\V1\Admin\Estimate\EstimatesController;
-use App\Http\Controllers\V1\Admin\Estimate\SendEstimateController;
 use App\Http\Requests\DeleteEstimatesRequest;
 use App\Http\Requests\EstimatesRequest;
 use App\Http\Requests\SendEstimatesRequest;
@@ -156,8 +155,8 @@ test('search estimates', function () {
 
 test('send estimate using a form request', function () {
     $this->assertActionUsesFormRequest(
-        SendEstimateController::class,
-        '__invoke',
+        EstimatesController::class,
+        'send',
         SendEstimatesRequest::class
     );
 });