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/Entity/Notification.php

@@ -22,7 +22,7 @@ class Notification
     #[ORM\Column(length: 255)]
     private ?string $message = null;
 
-    #[ORM\Column]
+    #[ORM\Column(name: 'is_read')]
     private bool $read = false;
 
     #[ORM\Column]