refactor: fix 7 CRUD system inconsistencies for robustness and maintainability

- Add user-assignment dependency check to DepartmentService.deleteByUuid (409 when users assigned)
- Standardize POST detection to isMethod('POST') in 10 create/edit actions
- Align RoleService code uniqueness to warning pattern (matching departments)
- Normalize repository create() return types from mixed to int|false (3 repos + 3 interfaces)
- Add JSON response branches to 4 non-user delete actions
- Document delete authorization ordering pattern
- Decompose AdminSettingsService.updateFromAdmin into domain-scoped private methods

Workflow: .agents/runs/CRUD-CONSISTENCY-001/
Reviewed by: Code Reviewer (pass), Security Reviewer (pass), Acceptance Tester (pass)
Quality gates: QG-001 PHPUnit pass, QG-002 PHPStan pass, QG-003 Architecture pass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Repository/Tenant/TenantRepository.php

@@ -127,7 +127,7 @@ class TenantRepository implements TenantRepositoryInterface
         return RepositoryArrayHelper::unwrap($row, 'tenants');
     }
 
-    public function create(array $data): mixed
+    public function create(array $data): int|false
     {
         return DB::insert(
             'insert into tenants (uuid, description, address, postal_code, city, country, region, vat_id, tax_number, phone, fax, email, support_email, support_phone, billing_email, website, privacy_url, imprint_url, primary_color, default_theme, allow_user_theme, status, status_changed_at, status_changed_by, created_by, created) values (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,NOW())',