Add a Publisher abstraction and queued job to publish from the UI

Introduce Publisher/PublisherManager (WordPress + Reddit implementations)
so publishing logic is shared between the CLI, the queue, and future
network integrations. Add a "Publish" button on the Posts page that
dispatches PublishPostJob instead of blocking the request — Reddit's
publisher shells out to the existing Playwright sidecar and can take
tens of seconds, so it can't run synchronously in a web request.

Adds a `target` field (e.g. subreddit) and `publishing` status to Post,
plus a `publish_error` field so failures surface in the UI. Refactors
posts:publish to delegate to WordPressPublisher without changing its
CLI output contract (existing tests pass unchanged).

Also fixes two bugs found along the way: UpdatePostRequest was silently
dropping `published_url` from PATCH requests (never in its validation
rules, despite AI_API.md documenting it), and three Livewire index-page
tests were broken by the earlier auth change (never re-run after adding
the `auth` middleware) since they hit routes via HTTP without a logged-in
user.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/Models/Post.php

@@ -15,7 +15,7 @@ class Post extends Model
         'tiktok', 'linkedin', 'youtube', 'blog', 'other',
     ];
 
-    public const STATUSES = ['draft', 'scheduled', 'published', 'failed'];
+    public const STATUSES = ['draft', 'scheduled', 'publishing', 'published', 'failed'];
 
     protected $fillable = [
         'site_id',
@@ -23,9 +23,11 @@ class Post extends Model
         'type',
         'title',
         'body',
+        'target',
         'status',
         'scheduled_at',
         'published_url',
+        'publish_error',
     ];
 
     protected $casts = [