fix(mail) : stop le spam GlitchTip de sync (double-encodage UTF7 + dossiers fantômes)

Deux causes racines généraient ~170 erreurs/cycle (toutes les 10 min) sur
la prod : "syncFolder[...] listMessages failed: Folder ... not found".

1. Double-encodage UTF7-IMAP : listFolders() stocke le chemin brut UTF7-IMAP,
   mais ImapMailProvider rappelait getFolder($path) qui ré-encode UTF8->UTF7-IMAP
   (webklex Client::getFolderByPath, utf7=false). Le caractère de shift "&" était
   ré-encodé, rendant introuvables les dossiers à accents/specials. Fix :
   getFolder($path, null, utf7: true) partout dans ImapMailProvider.

2. Dossiers fantômes jamais purgés : syncFolderStructure() gardait en DB les
   dossiers disparus du serveur, re-tentés à chaque cycle. Fix :
   syncFolderStructure() retourne le set des chemins présents sur le serveur ;
   doSyncAll() skip silencieusement les dossiers DB absents (conservés en DB
   pour les liens messages/tâches). Fallback historique si listFolders échoue.

Test : testSyncAllSkipsFoldersNoLongerPresentOnServer.

tests/Unit/Service/MailSyncServiceTest.php

@@ -132,6 +132,69 @@ class MailSyncServiceTest extends TestCase
         $service->syncFolderStructure();
     }
 
+    public function testSyncAllSkipsFoldersNoLongerPresentOnServer(): void
+    {
+        $config = new MailConfiguration();
+        $config->setEnabled(true);
+
+        $configRepo = $this->createMock(MailConfigurationRepositoryInterface::class);
+        $configRepo->method('findSingleton')->willReturn($config);
+
+        // The server only exposes INBOX; "Trash/STALE" was deleted remotely but
+        // still lingers in the DB.
+        $inboxDto = new MailFolderDto(
+            path: 'INBOX',
+            displayName: 'Inbox',
+            parentPath: null,
+            unreadCount: 0,
+            totalCount: 0,
+        );
+
+        $inboxFolder = new MailFolder();
+        $inboxFolder->setPath('INBOX');
+
+        $staleFolder = new MailFolder();
+        $staleFolder->setPath('Trash/STALE');
+
+        $provider = $this->createMock(MailProviderInterface::class);
+        $provider->method('listFolders')->willReturn([$inboxDto]);
+        // listMessages must only ever be called for INBOX, never the stale folder.
+        $provider->expects(self::once())
+            ->method('listMessages')
+            ->with('INBOX', 5000, 0)
+            ->willReturn([])
+        ;
+
+        $folderRepo = $this->createMock(MailFolderRepositoryInterface::class);
+        $folderRepo->method('findByPath')->willReturn($inboxFolder);
+        $folderRepo->method('findAllOrderedByPath')->willReturn([$inboxFolder, $staleFolder]);
+
+        $messageRepo = $this->createMock(MailMessageRepositoryInterface::class);
+        $messageRepo->method('findMaxUidInFolder')->willReturn(0);
+        $messageRepo->method('findAllUidsByFolder')->willReturn([]);
+        $messageRepo->method('findLastNByFolder')->willReturn([]);
+
+        $em = $this->createMock(EntityManagerInterface::class);
+        $em->method('isOpen')->willReturn(true);
+        $lockFactory = $this->makeLockFactory();
+
+        $service = new MailSyncService(
+            provider: $provider,
+            configRepository: $configRepo,
+            folderRepository: $folderRepo,
+            messageRepository: $messageRepo,
+            entityManager: $em,
+            lockFactory: $lockFactory,
+            logger: new NullLogger(),
+            managerRegistry: $this->createMock(ManagerRegistry::class),
+        );
+
+        $report = $service->syncAll();
+
+        self::assertSame(1, $report->foldersScanned);
+        self::assertSame([], $report->errors);
+    }
+
     public function testSyncFolderAbortsSuppressionWhenOver50Percent(): void
     {
         $config = new MailConfiguration();