Add Cross-Posting support for multiple social accounts

- Create post_social_account pivot table for many-to-many relationship
- Add migration to migrate existing social_account_id to pivot table
- Remove social_account_id column from posts table
- Update Post model with socialAccounts() BelongsToMany relationship
- Update Posts Livewire component to use array of selectedAccountIds
- Update Posts view with checkboxes for selecting multiple accounts
- Update PublishPostJob to iterate through all social accounts of matching type
- Update Publisher interface to accept optional SocialAccount parameter
- Update all Publishers (WordPress, Reddit, Twitter, LinkedIn) to support cross-posting
- Display multiple social accounts as badges in posts table

Now a single post can be published to multiple social accounts of the same type.
For example: a Twitter post can be published to multiple Twitter accounts.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

app/Jobs/PublishPostJob.php

@@ -21,7 +21,7 @@ class PublishPostJob implements ShouldQueue
 
     public function handle(PublisherManager $publishers): void
     {
-        $post = Post::with(['site', 'socialAccount'])->find($this->postId);
+        $post = Post::with(['site', 'socialAccounts'])->find($this->postId);
 
         if (! $post) {
             return;
@@ -34,6 +34,24 @@ class PublishPostJob implements ShouldQueue
             return;
         }
 
+        $results = [];
+        $errors = [];
+        $urls = [];
+
+        // Get all social accounts that match the post's type
+        $socialAccounts = $post->socialAccounts->filter(
+            fn ($account) => $account->network === $post->type
+        );
+
+        if ($socialAccounts->isEmpty()) {
+            $post->update([
+                'status' => 'draft',
+                'publish_error' => "No social accounts linked to this post for type '{$post->type}'.",
+            ]);
+
+            return;
+        }
+
         $publisher = $publishers->resolve($post);
 
         if (! $publisher) {
@@ -42,19 +60,39 @@ class PublishPostJob implements ShouldQueue
             return;
         }
 
-        $result = $publisher->publish($post);
+        // Publish to each social account
+        foreach ($socialAccounts as $socialAccount) {
+            $result = $publisher->publish($post, $socialAccount);
+            $results[] = $result;
 
-        if ($result->success) {
-            $post->update(['status' => 'published', 'published_url' => $result->url, 'publish_error' => null]);
+            if ($result->success) {
+                $urls[] = $result->url;
+            } else {
+                $errors[] = $result->error;
+            }
+        }
+
+        // If at least one succeeded, mark as published with the first URL
+        if (! empty($urls)) {
+            $post->update([
+                'status' => 'published',
+                'published_url' => $urls[0],
+                'publish_error' => ! empty($errors) ? implode('; ', $errors) : null,
+            ]);
 
             return;
         }
 
+        // All failed
         $post->update([
-            'status' => $result->attempted ? 'failed' : 'draft',
-            'publish_error' => $result->error,
+            'status' => 'failed',
+            'published_url' => null,
+            'publish_error' => implode('; ', $errors),
         ]);
 
-        Log::error('post publish failed', ['post_id' => $post->id, 'error' => $result->error]);
+        Log::error('post publish failed for all accounts', [
+            'post_id' => $post->id,
+            'errors' => $errors,
+        ]);
     }
 }