chore: add symfony/messenger + symfony/scheduler + phpunit infrastructure

- composer.json : symfony/messenger, symfony/scheduler, symfony/test-pack
- PHPStan fix : is_string() pour narrower mixed dans buildForecastGeometry
- phpunit.dist.xml + tests/bootstrap.php + bin/phpunit pour la suite de tests
- Suppression de src/Schedule.php (schedule vide généré par Flex, inutile)

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

backend/symfony.lock

@@ -79,6 +79,21 @@
             "ref": "5e490cc197fb6bb1ae22e5abbc531ddc633b6767"
         }
     },
+    "phpunit/phpunit": {
+        "version": "12.5",
+        "recipe": {
+            "repo": "github.com/symfony/recipes",
+            "branch": "main",
+            "version": "11.1",
+            "ref": "ca0bc067abfb40a8de1b2561b96cbfc2b833c314"
+        },
+        "files": [
+            ".env.test",
+            "phpunit.dist.xml",
+            "tests/bootstrap.php",
+            "bin/phpunit"
+        ]
+    },
     "symfony/console": {
         "version": "7.4",
         "recipe": {
@@ -124,6 +139,18 @@
             ".editorconfig"
         ]
     },
+    "symfony/messenger": {
+        "version": "7.4",
+        "recipe": {
+            "repo": "github.com/symfony/recipes",
+            "branch": "main",
+            "version": "6.0",
+            "ref": "d8936e2e2230637ef97e5eecc0eea074eecae58b"
+        },
+        "files": [
+            "config/packages/messenger.yaml"
+        ]
+    },
     "symfony/property-info": {
         "version": "7.4",
         "recipe": {
@@ -149,6 +176,18 @@
             "config/routes.yaml"
         ]
     },
+    "symfony/scheduler": {
+        "version": "7.4",
+        "recipe": {
+            "repo": "github.com/symfony/recipes",
+            "branch": "main",
+            "version": "7.2",
+            "ref": "caea3c928ee9e1b21288fd76aef36f16ea355515"
+        },
+        "files": [
+            "src/Schedule.php"
+        ]
+    },
     "symfony/security-bundle": {
         "version": "7.4",
         "recipe": {