Remove ShopWorker entity and migrate worker identity to ApplicationUser

Removes the ShopWorker and ShopWorkerRoleCost entities, all related DTOs,
mappings, controllers, views, and import/export paths. Worker identity is
now handled entirely through ApplicationUser with per-user LaborCostPerHour.
ShopWorkerRoleCosts table remains in production pending manual data migration.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Views/Help/Index.cshtml

@@ -189,22 +189,6 @@
         <!-- Shop Management -->
         <h2 class="h6 fw-semibold mb-2 text-muted text-uppercase" style="letter-spacing:.05em; font-size:.7rem;">Shop Management</h2>
         <div class="row g-3 mb-4">
-            <div class="col-md-6">
-                <div class="card border-0 shadow-sm h-100">
-                    <div class="card-body">
-                        <div class="d-flex align-items-start gap-3">
-                            <div class="rounded-3 bg-info bg-opacity-10 p-2 flex-shrink-0">
-                                <i class="bi bi-person-badge text-info fs-4"></i>
-                            </div>
-                            <div>
-                                <h5 class="card-title mb-1">Shop Workers</h5>
-                                <p class="card-text text-muted small mb-2">Add floor staff, assign roles like Coater or Sandblaster, and link workers to jobs and maintenance tasks.</p>
-                                <a asp-controller="Help" asp-action="ShopWorkers" class="btn btn-sm btn-outline-info">Read more <i class="bi bi-arrow-right ms-1"></i></a>
-                            </div>
-                        </div>
-                    </div>
-                </div>
-            </div>
             <div class="col-md-6">
                 <div class="card border-0 shadow-sm h-100">
                     <div class="card-body">