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/CompanyUsers/Edit.cshtml

@@ -106,6 +106,16 @@
                                 <input asp-for="Position" class="form-control" />
                                 <span asp-validation-for="Position" class="text-danger"></span>
                             </div>
+                            <div class="col-md-4">
+                                <label asp-for="LaborCostPerHour" class="form-label">Labor Cost Rate</label>
+                                <div class="input-group">
+                                    <span class="input-group-text">$</span>
+                                    <input asp-for="LaborCostPerHour" type="number" step="0.01" min="0" max="10000" class="form-control" placeholder="Use company default" />
+                                    <span class="input-group-text">/hr</span>
+                                </div>
+                                <span asp-validation-for="LaborCostPerHour" class="text-danger"></span>
+                                <small class="text-muted">Used for internal job costing only &mdash; never shown to customers. Overrides the company default when set. Leave blank to use the shop-wide rate.</small>
+                            </div>
                             <div class="col-md-6">
                                 <label asp-for="HireDate" class="form-label">Hire Date</label>
                                 <input asp-for="HireDate" class="form-control" type="date" />