Add Accountant role and CanManageBills/CanManageAccounting permissions

- AppConstants: add Accountant to CompanyRoles; add CanManageBills and
  CanManageAccounting to Policies
- ApplicationUser: add CanManageBills and CanManageAccounting bool fields
- UserManagementDtos: expose new fields in all three DTOs
- ClaimsPrincipalFactory: emit ManageBills and ManageAccounting claims
- Program.cs: add CanManageBills and CanManageAccounting policies;
  update CanManageInvoices, CanViewReports, CanManagePurchaseOrders,
  and CanManageVendors to auto-pass for Accountant role
- BillsController: replace CanManageInventory with CanManageBills on
  all write actions (correct policy — bills are not inventory)
- BankReconciliationsController: replace CanManageJobs with
  CanManageAccounting on write actions
- CompanyUsersController: add Accountant to validCompanyRoles (both
  Create/Edit), legacyRole switch, and all permission assignment blocks
- Create/Edit views: add Accountant option to role dropdown; add
  CanManageBills and CanManageAccounting checkboxes; JS auto-checks
  financial permissions when Accountant role is selected
- Migration AddAccountantRolePermissions: adds columns + backfills
  CanManageBills=1 and CanManageAccounting=1 for all CompanyAdmin users

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

src/PowderCoating.Application/DTOs/User/UserManagementDtos.cs

@@ -41,6 +41,8 @@ public class CompanyUserDto
     public bool CanManageMaintenance { get; set; }
     public bool CanManageInvoices { get; set; }
     public bool CanViewReports { get; set; }
+    public bool CanManageBills { get; set; }
+    public bool CanManageAccounting { get; set; }
 }
 
 /// <summary>
@@ -156,6 +158,12 @@ public class CreateCompanyUserDto
     [Display(Name = "Can View Reports")]
     public bool CanViewReports { get; set; }
 
+    [Display(Name = "Can Manage Bills & AP")]
+    public bool CanManageBills { get; set; }
+
+    [Display(Name = "Can Manage Accounting")]
+    public bool CanManageAccounting { get; set; }
+
     [Display(Name = "Send Welcome Email")]
     public bool SendWelcomeEmail { get; set; } = true;
 }
@@ -258,4 +266,10 @@ public class UpdateCompanyUserDto
 
     [Display(Name = "Can View Reports")]
     public bool CanViewReports { get; set; }
+
+    [Display(Name = "Can Manage Bills & AP")]
+    public bool CanManageBills { get; set; }
+
+    [Display(Name = "Can Manage Accounting")]
+    public bool CanManageAccounting { get; set; }
 }