fix: address code review issues

- Rename `read` column to `is_read` (PostgreSQL reserved word)
- Wrap navbar + modal in parent div for Stimulus controller scope
- Set temporary filePath before first flush in ImportController
- Use RETURNING clause for atomic incrementProcessedBatches
- Return proper empty 204 response in NotificationController

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

src/Repository/ImportRepository.php

@@ -20,13 +20,8 @@ class ImportRepository extends ServiceEntityRepository
 
     public function incrementProcessedBatches(Import $import): int
     {
-        $this->getEntityManager()->getConnection()->executeStatement(
-            'UPDATE import SET processed_batches = processed_batches + 1 WHERE id = :id',
-            ['id' => $import->getId()]
-        );
-
         return (int) $this->getEntityManager()->getConnection()->fetchOne(
-            'SELECT processed_batches FROM import WHERE id = :id',
+            'UPDATE import SET processed_batches = processed_batches + 1 WHERE id = :id RETURNING processed_batches',
             ['id' => $import->getId()]
         );
     }