feat(blog): add city_id to blogs for city-specific scoping

- Introduced a new nullable city_id column in the blogs table to allow scoping of blog posts to specific cities.
- Updated Blog entity to include a ManyToOne relationship with the City entity.
- Enhanced BlogController to handle city_id in the request, allowing filtering of posts by city.
- Modified BlogRepository to support querying published posts based on city_id.
- Added tests to ensure correct behavior for city-scoped and nationwide posts, including creation and updating of posts with city associations.

migrations/Version20260719044321.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Blog posts get an optional city so the multi-domain public site can scope them.
+ * NULL is a permanent, meaningful state: a nationwide post, canonical on the main
+ * domain and listed on every city domain.
+ *
+ * Existing rows become nationwide, which preserves current behaviour.
+ *
+ * Note: doctrine:migrations:diff also wanted to alter date_overrides,
+ * patient_sessions, wallet_transactions and weekly_schedules. That is
+ * pre-existing drift between the entities and the database, unrelated to this
+ * feature, so it is deliberately left out rather than bundled in here.
+ */
+final class Version20260719044321 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add nullable blogs.city_id (NULL = nationwide post)';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE blogs ADD city_id INT DEFAULT NULL');
+        $this->addSql('ALTER TABLE blogs ADD CONSTRAINT FK_F41BCA708BAC62AF FOREIGN KEY (city_id) REFERENCES cities (id) ON DELETE SET NULL');
+        $this->addSql('CREATE INDEX idx_blogs_city ON blogs (city_id)');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE blogs DROP FOREIGN KEY FK_F41BCA708BAC62AF');
+        $this->addSql('DROP INDEX idx_blogs_city ON blogs');
+        $this->addSql('ALTER TABLE blogs DROP city_id');
+    }
+}