feat(blog): add SEO fields, scheduling, and representative ownership to blog posts

- Introduced new SEO fields (meta_title, meta_description, primary_keyword, secondary_keywords, faq, internal_links, external_links, reading_time, canonical_url, og_image) to the Blog entity.
- Added scheduling capability with a scheduled_at field to manage automatic publishing of blog posts.
- Implemented representative ownership through a foreign key representation_id in the Blog entity, allowing representatives to manage their own posts.
- Updated BlogController and RepresentationBlogController to handle new fields and ensure proper data handling for SEO and scheduling.
- Created BlogWriter service to encapsulate the logic for applying SEO and scheduling fields to blog entities.
- Added PublishScheduledBlogsMessage and its handler to manage the publishing of scheduled blogs.
- Implemented ScheduledBlogPublisher service to publish drafts whose scheduled_at has arrived, respecting review status.
- Created migration to update the database schema with new fields and constraints.
- Added tests to ensure the correct functionality of new features, including SEO fields, representative scope, and scheduled publishing.

src/Blog/Service/ScheduledBlogPublisher.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace App\Blog\Service;
+
+use App\Blog\Entity\Blog;
+use App\Blog\Repository\BlogRepository;
+
+/**
+ * Publishes drafts whose scheduled_at has arrived. A post in the review workflow
+ * is published only once review_status = approved — the medical-review gate wins
+ * over the schedule, so AI-generated content is never auto-published unreviewed.
+ */
+class ScheduledBlogPublisher
+{
+    public function __construct(private readonly BlogRepository $blogRepo) {}
+
+    /** @return int number of posts published */
+    public function publishDue(?int $now = null): int
+    {
+        $now = $now ?? time();
+        $due = $this->blogRepo->findDueForPublish($now);
+        foreach ($due as $blog) {
+            $blog->setStatus(Blog::STATUS_PUBLISHED);
+            $this->blogRepo->save($blog);
+        }
+        return count($due);
+    }
+}