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>

pages/admin/permissions/edit($id).php

@@ -54,7 +54,7 @@ if ($request->isMethod('POST') && !Session::checkCsrfToken()) {
     return;
 }
 
-if ($request->hasBody('key')) {
+if ($request->isMethod('POST')) {
     $submitDecision = $authorizationService->authorize(PermissionAuthorizationPolicy::ABILITY_ADMIN_PERMISSIONS_EDIT_SUBMIT, [
         'actor_user_id' => $currentUserId,
         'target_permission_id' => $id,