Add employee-to-order assignments with FR-EM-3 conflict validation

Adds the Assignment core object (Order x Employee, date range) with full
CRUD, soft-delete/trash integration, and generated API clients.

Layers FR-EM-3 conflict checks onto assignment creation: qualification,
absence/availability, working-hours approximation, cross-order overlap,
and active-contract coverage. Each check's severity (Warning vs. Error)
is configurable at runtime via a new AssignmentValidationSettings
singleton and admin settings panel, instead of being hardcoded - lets
the business tune strictness per check without a redeploy.

Adds a live GET /api/assignments/check endpoint so the create-assignment
dialog can preview conflicts as the user picks employee/dates, before
they hit save, rather than only finding out after submitting.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

omsorgWeb/mitarbeiter-app/api-client-php/test/Api/AssignmentValidationSettingsApiTest.php

@@ -0,0 +1,97 @@
+<?php
+/**
+ * AssignmentValidationSettingsApiTest
+ * PHP version 8.1
+ *
+ * @category Class
+ * @package  OmsorgCoreClient
+ * @author   OpenAPI Generator team
+ * @link     https://openapi-generator.tech
+ */
+
+/**
+ * OmsorgCore.Api
+ *
+ * No description provided (generated by Openapi Generator https://github.com/openapitools/openapi-generator)
+ *
+ * The version of the OpenAPI document: 1.0
+ * Generated by: https://openapi-generator.tech
+ * Generator version: 7.14.0
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Please update the test case below to test the endpoint.
+ */
+
+namespace OmsorgCoreClient\Test\Api;
+
+use \OmsorgCoreClient\Configuration;
+use \OmsorgCoreClient\ApiException;
+use \OmsorgCoreClient\ObjectSerializer;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * AssignmentValidationSettingsApiTest Class Doc Comment
+ *
+ * @category Class
+ * @package  OmsorgCoreClient
+ * @author   OpenAPI Generator team
+ * @link     https://openapi-generator.tech
+ */
+class AssignmentValidationSettingsApiTest extends TestCase
+{
+
+    /**
+     * Setup before running any test cases
+     */
+    public static function setUpBeforeClass(): void
+    {
+    }
+
+    /**
+     * Setup before running each test case
+     */
+    public function setUp(): void
+    {
+    }
+
+    /**
+     * Clean up after running each test case
+     */
+    public function tearDown(): void
+    {
+    }
+
+    /**
+     * Clean up after running all test cases
+     */
+    public static function tearDownAfterClass(): void
+    {
+    }
+
+    /**
+     * Test case for apiSettingsAssignmentValidationGet
+     *
+     * .
+     *
+     */
+    public function testApiSettingsAssignmentValidationGet()
+    {
+        // TODO: implement
+        self::markTestIncomplete('Not implemented');
+    }
+
+    /**
+     * Test case for apiSettingsAssignmentValidationPut
+     *
+     * .
+     *
+     */
+    public function testApiSettingsAssignmentValidationPut()
+    {
+        // TODO: implement
+        self::markTestIncomplete('Not implemented');
+    }
+}