feat: replace notifications with import status in profile dropdown

Remove the notification system entirely and show import progress
directly in the user dropdown menu. Block new imports while one
is already running.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/Version20260331000001.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260331000001 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Drop notification table';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('DROP TABLE IF EXISTS notification');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql(<<<'SQL'
+            CREATE TABLE notification (
+                id SERIAL PRIMARY KEY,
+                user_id INT NOT NULL REFERENCES "user"(id),
+                message VARCHAR(255) NOT NULL,
+                is_read BOOLEAN NOT NULL DEFAULT FALSE,
+                created_at TIMESTAMP(0) WITHOUT TIME ZONE NOT NULL
+            )
+        SQL);
+        $this->addSql('COMMENT ON COLUMN notification.created_at IS \'(DC2Type:datetime_immutable)\'');
+    }
+}